Projects/Mailserver with Debian, Exim, spamassassin, greylistd, DKIM, SRS, SPF, DMARC, forwarding, LDAP, dovecot, LMTP, disk crypto
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| Project Mailserver with Debian, Exim, spamassassin, greylistd, DKIM, SRS, SPF, DMARC, forwarding, LDAP, dovecot, LMTP, disk crypto | |
| Name | Mailserver with Debian, Exim, spamassassin, greylistd, DKIM, SRS, SPF, DMARC, forwarding, LDAP, dovecot, LMTP, disk crypto |
| Start | 2015/03/01 |
| End | |
| Contact | WilcoBaanHofman |
| Website | |
| Information | This page describes how we set up our mail system and how other people can set up their own full blown modern mail servers. |
| Status | Production |
This page will talk about how to set up a mail server, and also how to comply with Google mail / gmail's bizarre, idiotic IPv6 spam policies.
You will need an SPF policy, DKIM and a valid forward/reverse DNS which matches the EHLO your mailserver sends. You will need spam filtering, virus filtering and a valid TLS connection.
TODO
- Running an external (partial) LDAP slave
Prerequisites
- A (virtual) machine running Debian wheezy or jessie with public IPv4 and IPv6 internet connectivity
- Possibility to set up reverse DNS for your IPv4 and IPv6 addresses
- Ability to have a CA sign your certificates (can be done for free at StartSSL).
Determine your setup
What kind of setup are you going to run?
- Single mailserver
- MTA + Encrypted mail store
- High-availability setup
Single mailserver
In this case, install all packages on the same machine, do not use disk encryption, because your mail server will be unreachable after a power failure.
MTA + Encrypted mail store
This is the best scenario for small setups and requires two (virtual) machines, one MTA that handles accepting of emails and spam/virus filtering and one machine that is encrypted. This guide covers this setup. To prepare for this setup, simple install one machine without disk crypto and one with. The MTA will hold mail for up to 3 weeks if you haven't typed your disk crypto password on boot yet (See the lmtp section).
The setup will look like this:
High-availability
Running MTAs in high availability is easy, just duplicate the MTA setup and add two MX records to your domains. (Of course, your bayesian spam filters may train differently..). Running dovecot in high-availability is a different story..
The safest way to run dovecot in high-availibility mode is to run the mail store on top of a high-performance redundant NAS. This can be a proprietary NAS or some open source HA NFS setup. You will need shared NFS storage. The best performing mailbox format is mdbox, but this is also the easiest store to corrupt the indexes of if two nodes write to it in parallel. Locking may cause performance degradation and has to work reliably on your NFS backend, otherwise the indexes get corrupted. To prevent index corruption and locking overhead, there is the director component, which will pin a user to a node as long as that node is up. The dovecot part of this setup is *not* included in this guide (yet).
This setup will look like this:
Install the packages
Step 1: Install the required packages
~# apt-get install exim4-daemon-heavy spamassassin clamav-daemon greylistd spf-tools-perl sasl2-bin srs pyzor razor
If you want to run a mailing list server as well, also install mailman and apache2.
~# apt-get install mailman apache2
If dovecot is going to run on this same host (you're not doing high-availability or full disk crypto mail store), also install dovecot-imapd, dovecot-ldap and dovecot-lmtpd on the mta. Otherwise, do this on the host(s) where you want to run your dovecot.
~# apt-get install dovecot-imapd dovecot-ldap dovecot-lmtpd dovecot-sieve dovecot-managesieved
Verify that no interfering packages are installed (like postfix, sendmail, amavis)
~$ dpkg -l |egrep '(postfix|sendmail|amavis)'
This command should give no output, if it does and starts with ii, remove that package.
Configuring exim4
~# dpkg-reconfigure exim4-config
Choose internet site, set the host name to the value you will set the reverse DNS to, specify all domains you want to receive mail for and choose split files (unless you want to replace every exim4 file name here with exim4.conf.template in this manual).
Testing Exim4
Now try to see if simple address resolution works. This will only test against local system users. It's good to test this, even if you're going to add LDAP later. Substitute the IP and mail addresses for your own stuff. For now, you can test any local system user @ one of the domains you accepted.
Any line not starting with a number is something you have to type yourself to test this.
~$ telnet 2a02:2ca0:aaa::a843:657d 25 Trying 2a02:2ca0:aaa::a843:657d... Connected to 2a02:2ca0:aaa::a843:657d. Escape character is '^]'. 220 mail.bitlair.nl ESMTP Exim 4.80 Sun, 15 Mar 2015 12:37:27 -0400 EHLO mail.bitlair.nl 250-mail.bitlair.nl Hello mail.bitlair.nl [2a02:2ca0:aaa::a843:657d] 250-SIZE 52428800 250-8BITMIME 250-PIPELINING 250-STARTTLS 250 HELP MAIL FROM: <wilco@bitlair.nl> 250 OK RCPT TO: <wilco@bitlair.nl> 250 Accepted RCPT TO: <aoeu@bitlair.nl> 550 Unrouteable address QUIT
TLS
Hint: StartCom signs certificates for free. Class 2 certification allows you do much more, though. In order to qualify for level 2 verification, do a personal validation once a year for $59 and you can issue an unlimited number of certificates for personal use. For business use, it requires an additional $59 for organisation verification on top of the personal validation. Your account will be converted to a business account, so no more personal certificates on that account.
To generate the key and certificate signing request (replace mail.bitlair.nl with your Fully Qualified Domain Name):
~# openssl req -sha256 -days 3650 -nodes -new -newkey rsa:4096 -keyout /etc/ssl/private/mail.bitlair.nl-key.pem -out /etc/ssl/mail.bitlair.nl-csr.pem
Input your location and contact information. At the Common Name field, input your mail hostname (mail.bitlair.nl in my case). Do not enter a challenge password.
Copy the certificate signing request to a CA for signing. Allow the CA to sign it, then you'll receive a certificate from the CA. Place the received certificate in /etc/ssl/mail.your.domain-cert.pem
Put MAIN_TLS_ENABLE=yes near the top in /etc/exim4/conf.d/main/03_exim4-config_tlsoptions and set the following keys:
MAIN_TLS_CERTIFICATE = /etc/ssl/mail.bitlair.nl-cert.pem MAIN_TLS_PRIVATEKEY = /etc/ssl/private/mail.bitlair.nl-key.pem
Create the ssl-cert group, allow this group to read in /etc/ssl/private and add the exim user to the ssl-cert group to make sure exim can read the private key:
~# groupadd --system ssl-cert ~# chgrp ssl-cert /etc/ssl/private ~# chmod 750 /etc/ssl/private ~# usermod -a -G ssl-cert Debian-exim
Download your chain file from your CA. If you have a startcom class 1 certificate, find the startcom sha256 class1 server ca pem file online. The file is called sub.class1.server.sha1.ca.pem and can be found at [1]. Store the chain file in /etc/ssl/.
Now append its content to /etc/ssl/your-domain-cert.pem. I have a class 2 certificate, so I used this command:
~# cat /etc/ssl/sub.class2.server.sha2.ca.pem >> /etc/ssl/mail.bitlair.nl-cert.pem
Regenerate the configuration and restart exim:
~# update-exim4.conf ~# service exim4 restart
Testing STARTTLS
~$ telnet 2a02:2ca0:aaa::a843:657d 25 Trying 2a02:2ca0:aaa::a843:657d... Connected to 2a02:2ca0:aaa::a843:657d. Escape character is '^]'. 220 mail.bitlair.nl ESMTP Exim 4.80 Sun, 15 Mar 2015 12:37:10 -0400 EHLO mail.bitlair.nl 250-mail.bitlair.nl Hello mail.bitlair.nl [2a02:2ca0:aaa::a843:657d] 250-SIZE 52428800 250-8BITMIME 250-PIPELINING 250-STARTTLS 250 HELP STARTTLS 220 TLS go ahead
STARTTLS should be listed and give a 220 status code.
Testing TLS
Unfortunately, openssl s_client does not support IPv6, but this the tests the legacy IP listener as well as TLS:
~$ openssl s_client -connect mail.bitlair.nl:25 -starttls smtp -verify 5 -CAfile /etc/ssl/certs/ca-certificates.crt
New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA256
Server public key is 1024 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol : TLSv1.2
Cipher : DHE-RSA-AES256-SHA256
Session-ID: 82CBCEC7833853A674F6399694A03052566C494E1F6DDC8DE2CD4B3A9F8ED528
Session-ID-ctx:
Master-Key: BAE67F5D50E5C1C95FBDF355C1BDE18C6251E13F5B8686977292A54657498EFECFF518290211F24F01C40E39929981C4
Key-Arg : None
PSK identity: None
PSK identity hint: None
SRP username: None
Start Time: 1426438799
Timeout : 300 (sec)
Verify return code: 0 (ok)
This should give Verify return code 0 at all times. Anything else is wrong.. see the troubleshooting section.
SASL Authenticated relay
To enable relaying of messages after authentication, for SPF or just for laptops that are on different connections all the time, SASL authentication needs to be enabled.
Enabling other ports than 25
Port 25 is usually blocked by firewalls, for good reason. An alternative authenticated-only submission port exists on port 587 and a legacy TLS on connect port on 465 also exists.
To enable these, set the following in /etc/default/exim4:
SMTPLISTENEROPTIONS='-oX 25:465:587 -oP /var/run/exim4/exim.pid'
And in /etc/exim4/conf.d/main/03_exim4-config_tlsoptions add the following near the top:
tls_on_connect_ports=465
Regenerate the configuration and restart exim:
~# update-exim4.conf ~# service exim4 restart
SASL authentication
Set the following to /etc/default/saslauthd, this is the default these days
START=yes
Start saslauthd.
~# service saslauthd start
In /etc/exim4/conf.d/auth/30_exim4-config_examples, uncomment the section:
plain_saslauthd_server:
driver = plaintext
public_name = PLAIN
server_condition = ${if saslauthd{{$auth2}{$auth3}}{1}{0}}
server_set_id = $auth2
server_prompts = :
.ifndef AUTH_SERVER_ALLOW_NOTLS_PASSWORDS
server_advertise_condition = ${if eq{$tls_cipher}{}{}{*}}
.endif
login_saslauthd_server:
driver = plaintext
public_name = LOGIN
server_prompts = "Username:: : Password::"
# don't send system passwords over unencrypted connections
server_condition = ${if saslauthd{{$auth1}{$auth2}}{1}{0}}
server_set_id = $auth1
.ifndef AUTH_SERVER_ALLOW_NOTLS_PASSWORDS
server_advertise_condition = ${if eq{$tls_cipher}{}{}{*}}
.endif
Add the Debian-exim user to the sasl group.
~# usermod -a -G sasl Debian-exim
Regenerate the configuration and restart exim:
~# update-exim4.conf ~# service exim4 restart
Testing
~$ swaks -a -tls -q AUTH -s 2a02:2ca0:aaa::a843:657d -au username Password: enter_your_password === Trying 2a02:2ca0:aaa::a843:657d:25... === Connected to 2a02:2ca0:aaa::a843:657d. <- 220 mail.bitlair.nl ESMTP Exim 4.80 Sun, 15 Mar 2015 16:04:35 -0400 -> EHLO mail.bitlair.nl <- 250-mail.bitlair.nl Hello mail.bitlair.nl [2a02:2ca0:aaa::a843:657d] <- 250-SIZE 52428800 <- 250-8BITMIME <- 250-PIPELINING <- 250-STARTTLS <- 250 HELP -> STARTTLS <- 220 TLS go ahead === TLS started w/ cipher DHE-RSA-AES256-SHA256 === TLS peer subject DN="/C=NL/ST=Utrecht/L=Amersfoort/O=Stichting Bitlair/CN=mail.bitlair.nl" ~> EHLO mail.bitlair.nl <~ 250-mail.bitlair.nl Hello mail.bitlair.nl [2a02:2ca0:aaa::a843:657d] <~ 250-SIZE 52428800 <~ 250-8BITMIME <~ 250-PIPELINING <~ 250-AUTH PLAIN LOGIN <~ 250 HELP ~> AUTH LOGIN <~ 334 VXNlcm5hbWU6 ~> d2lsY28= <~ 334 UGFzc3dvcmQ6 ~> YmxpZXA= <~ 235 Authentication succeeded ~> QUIT <~ 221 mail.bitlair.nl closing connection Connection closed with remote host.
Authentication succeeded is what you want!
DNS block lists
Add CHECK_RCPT_IP_DNSBLS to the top of /etc/exim4/conf.d/acl/30_exim4-config_check_rcpt, like my list of DNSBLs:
CHECK_RCPT_IP_DNSBLS=cbl.abuseat.org:sbl-xbl.spamhaus.org:psbl.surriel.com:b.barracudacentral.org:dul.dnsbl.sorbs.net:spamsources.fabel.dk
Remove the whole ifdef CHECK_RCPT_IP_DNSBLS section from /etc/exim4/conf.d/acl/30_exim4-config_check_rcpt and place the following section just before the accept rule with relay_to_domains
accept
domains = +local_domains +relay_to_domains
dnslists = list.dnswl.org
logwrite = $sender_host_address is whitelisted
deny
message = ${sender_host_address} is listed at ${dnslist_domain}; See ${dnslist_text}
!hosts = +relay_from_hosts
!authenticated = *
dnslists = CHECK_RCPT_IP_DNSBLS
Regenerate the configuration and restart exim:
~# update-exim4.conf ~# service exim4 restart
More information exim4 configuration
- http://www.exim.org/exim-html-current/doc/html/spec_html/ch-string_expansions.html
- http://www.exim.org/exim-html-current/doc/html/spec_html/
Spamassassin
Spamassassin configuration
To enable spamd from spamassassin, set the following in /etc/default/spamassassin (these may already be the default):
ENABLED=1
And add "-u debian-spamd" to the options, you will get something like:
OPTIONS="--create-prefs --max-children 5 --helper-home-dir -u debian-spamd"
And also enable the cron rules updates by setting
CRON=1
You will probably want more terse spam reporting, because it will be in the email headers, to get this, add the following to /etc/spamassassin/local.cf:
clear_report_template report _YESNO_, score=_SCORE_ required=_REQD_ autolearn=_AUTOLEARN_ report tests=_TESTSSCORES
While you're there, you may want to enable the bayesian classifier, and set up razor and pyzor, and fix RFC-ignorant rules.
# Use Bayesian classifier (default: 1) # use_bayes 1 # Bayesian classifier auto-learning (default: 1) # bayes_auto_learn 1 bayes_auto_learn_threshold_nonspam -0.001 bayes_auto_learn_threshold_spam 8.0 # Use razor and pyzor use_razor2 1 use_pyzor 1 # Disable stupid RFC-incompatible spamassassin SPF_NEUTRAL check. Do not add points for SPF_NEUTRAL, as it should be treated the same as having no SPF record. score SPF_NEUTRAL 0
Now, set up razor and pyzor:
~# razor-admin -home=/etc/mail/spamassassin/.razor -create ~# razor-admin -home=/etc/mail/spamassassin/.razor -register ~# razor-admin -home=/etc/mail/spamassassin/.razor -discover ~# pyzor --homedir /etc/mail/spamassassin discover
Restart spamassassin.
~# service spamassassin restart
Exim spamd integration
Uncomment the following line in /etc/exim4/conf.d/main/02_exim4-config_options:
spamd_address = 127.0.0.1 783
In /etc/exim4/conf.d/acl/40_exim4-config_check_data, uncomment the following section:
# warn # spam = Debian-exim:true # add_header = X-Spam_score: $spam_score\n\ # X-Spam_score_int: $spam_score_int\n\ # X-Spam_bar: $spam_bar\n\ # X-Spam_report: $spam_report
Also replace Debian-exim with debian-spamd (case sensitive), change _report to -Status and dash/upper case the rest (See section below for result). To bounce messages, also add this directly below:
deny
message = This message scored $spam_score spam points.
spam = debian-spamd
condition = ${if >{$spam_score_int}{76}{1}{0}}
You'll get something like this:
warn
spam = debian-spamd:true
add_header = X-Spam-Score: $spam_score\n\
X-Spam-Score-Int: $spam_score_int\n\
X-Spam-Bar: $spam_bar\n\
X-Spam-Status: $spam_report
deny
message = This message scored $spam_score spam points.
spam = debian-spamd
condition = ${if >{$spam_score_int}{76}{1}{0}}
Regenerate the configuration and restart exim:
~# update-exim4.conf ~# service exim4 restart
Testing spam blocking
$ telnet 127.0.0.1 25 Trying 127.0.0.1... Connected to 127.0.0.1. Escape character is '^]'. 220 mail.bitlair.nl ESMTP Exim 4.80 Sun, 15 Mar 2015 13:53:46 -0400 EHLO mail.bitlair.nl 250-mail.bitlair.nl Hello localhost.localdomain [127.0.0.1] 250-SIZE 52428800 250-8BITMIME 250-PIPELINING 250-STARTTLS 250 HELP MAIL FROM: <wilco@bitlair.nl> 250 OK RCPT TO: <wilco@bitlair.nl> 250 Accepted DATA 354 Enter message, ending with "." on a line by itself Subject: test XJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-ANTI-UBE-TEST-EMAIL*C.34X . 550 This message scored 1002.6 spam points.
You should get error 550 here.
More information on spamassassin
- http://michaelfranzl.com/2013/09/07/setting-up-exim4-mail-transfer-agent-with-spam-filtering-greylisting-and-anti-virus/
- https://spamassassin.apache.org/
Antivirus
Setting up ClamAV
Update the antivirus database:
~# freshclam ClamAV update process started at Sun Mar 15 13:57:01 2015 main.cvd is up to date (version: 55, sigs: 2424225, f-level: 60, builder: neo) daily.cvd is up to date (version: 20194, sigs: 1348078, f-level: 63, builder: dgoddard) bytecode.cvd is up to date (version: 247, sigs: 41, f-level: 63, builder: dgoddard)
You will get a message about outdated ClamAV if you do not have the latest version from stable-updates. Make sure you have it in your sources list and preferably in the unattended-upgrades list. Also see the troubleshooting section.
If you get a message about freshclam.log being locked, this means the clamav database is already up to date, check the freshclam.log for any warnings, like "your version is OUTDATED".
Add clamav to the Debian-exim group, so that clamav-daemon can read the message to scan.
~# usermod -a -G Debian-exim clamav
In /etc/clamav/clamd.conf set clamav to use the supplementary group:
AllowSupplementaryGroups true
Restart clamav-daemon
~# service clamav-daemon restart
Exim clamd integration
In /etc/exim4/conf.d/main/02_exim4-config_options, uncomment the following line:
av_scanner = clamd:/var/run/clamav/clamd.ctl
In /etc/exim4/conf.d/acl/40_exim4-config_check_data, uncomment the following section
deny
malware = *
message = This message was detected as possible malware ($malware_name).
Regenerate the exim4 config and restart exim.
~# update-exim4.conf ~# service exim4 restart
Testing
~$ telnet 2a02:2ca0:aaa::a843:657d 25 Trying 2a02:2ca0:aaa::a843:657d... Connected to 2a02:2ca0:aaa::a843:657d. Escape character is '^]'. 220 mail.bitlair.nl ESMTP Exim 4.80 Sun, 15 Mar 2015 14:10:10 -0400 EHLO mail.bitlair.nl 250-mail.bitlair.nl Hello mail.bitlair.nl [2a02:2ca0:aaa::a843:657d] 250-SIZE 52428800 250-8BITMIME 250-PIPELINING 250-STARTTLS 250 HELP MAIL FROM: <wilco@bitlair.nl> 250 OK RCPT TO: <wilco@bitlair.nl> 250 Accepted DATA 354 Enter message, ending with "." on a line by itself Subject: test X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H* . 550 This message was detected as possible malware (Eicar-Test-Signature).
You should get error 550 here. This is good.
More information on ClamAV
- http://michaelfranzl.com/2013/09/07/setting-up-exim4-mail-transfer-agent-with-spam-filtering-greylisting-and-anti-virus/
- http://www.exim.org/exim-html-current/doc/html/spec_html/ch-content_scanning_at_acl_time.html
- http://www.clamav.net/index.html
Setting up DKIM
Contrary to SPF and DMARC, DKIM is actually a good idea. This does not break the internet, I advise everyone to implement DKIM.
Configuring exim for DKIM
The first step to getting DKIM working, is generating an RSA key for DKIM. You will be tempted to use a large key here, but given that you have to add the public key to DNS, do not use more than 1024-bit keys. If you want to use stronger cryptography for this in the future, please consider contributing to the support of ECC crypto in DKIM.
~# mkdir -m 0750 /etc/exim4/dkim_keys ~# chown root:Debian-exim /etc/exim4/dkim_keys
To generate the RSA key pair (repeat per domain):
~# openssl genrsa -out /etc/exim4/dkim_keys/bitlair.nl.private.pem 1024 ~# openssl rsa -in /etc/exim4/dkim_keys/bitlair.nl.private.pem -out /etc/exim4/dkim_keys/bitlair.nl.public.pem -pubout -outform PEM
Add the following to the top of /etc/exim4/conf.d/transport/30_exim4-config_remote_smtp:
DKIM_DOMAIN = ${domain:$return_path}
DKIM_SELECTOR = exim
DKIM_FILE = /etc/exim4/dkim_keys/${lc:${domain:$return_path}}.private.pem
DKIM_PRIVATE_KEY = ${if exists{DKIM_FILE}{DKIM_FILE}{0}}
DKIM_CANON = relaxed
DKIM_STRICT = true
Configuring DNS for DKIM
Update your DNS zones to have the following records:
exim._domainkey IN TXT v=DKIM1; k=rsa; p=MIGfMA... <- your base64-encoded public key here _domainkey IN TXT o=~;
Regenerate the configuration and restart exim:
~# update-exim4.conf ~# service exim4 restart
Testing
Send an email to yourself from your MTA, you should see DKIM headers added to your message, to verify if it really checks out, send an email to check-auth@verifier.port25.com from your MTA.
It should respond with something like:
DKIM check: pass
More information on DKIM
- http://michaelfranzl.com/2013/09/07/setting-up-exim4-mail-transfer-agent-with-spam-filtering-greylisting-and-anti-virus/
- http://www.iodigitalsec.com/exim-dkim-and-debian-configuration/
- http://mikepultz.com/2010/02/using-dkim-in-exim/
- https://www.debian-administration.org/users/lee/weblog/41
- http://www.dkim.org/
SPF
Please note, before you add SPF: SPF is very broken. It assumes that people do not forward e-mail. It breaks .forward files, procmail forwards, etc. There is a remedy, called Sender Rewriting Scheme, but people are generally not aware of this. If you want to forward to gmail.com, which is known broken, because it mandates SPF records.
Adding SPF to your domain
You can set limits on who can send on behalf of your domain using DNS. However, extremely few mail forwards have implemented SRS. As stated on wikipedia: "Publishers of SPF FAIL policies must accept the risk that their legitimate emails are being rejected or bounced. They should test (e.g., with a SOFTFAIL policy) until they are satisfied with the results.".
Unfortunately, adding SPF to your domain adds to the legitimacy of your domain, and will decrease your chances of getting into a spam box. So it would be wise to set an SPF policy of allowing your mailservers and hosts under your domain, but leave the rest neutral with ?all. -all is guaranteed to break plain mail forwarding. ~all will make sure your mail reaches the spam box.
To have an SPF policy, I advise to not use any fails on your domain, but configure a record like:
@ IN TXT "v=spf1 a mx ?all"
This will ensure that hosts under your domain can pass SPF, as can your mailservers, but it is neutral for other, potentially forwarding hosts.
Adding Sending Rewriting Scheme (SRS)
Be careful with mail forwards, make sure your spam rules are set strictly enough, because your mail server reputation with gmail depends on forwarding mostly non-spam. If you want to do mail forwards to gmail, you need to implement SRS, because gmail on IPv6 is a known broken SPF mail system.
Installing srsd
Create /etc/init.d/srsd with content:
#! /bin/sh
### BEGIN INIT INFO
# Provides: srsd
# Required-Start:
# Required-Stop:
# Should-Start:
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: SRS daemon
# Description: SRS daemon
### END INIT INFO
set -e
# /etc/init.d/srsd: start and stop the srsd daemon
DAEMON=/usr/bin/srsd
USER=Debian-exim
SECRETFILE=/etc/srsd.secret
PIDFILE=/var/run/srsd.pid
SOCKETFILE=/tmp/srsd
SRSD_OPTS="--secretfile ${SECRETFILE}"
test -x $DAEMON || exit 0
. /lib/lsb/init-functions
srsd_start() {
if start-stop-daemon --start --quiet --background \
--chuid $USER \
--pidfile $PIDFILE --make-pidfile \
--exec $DAEMON \
-- $SRSD_OPTS
then
rc=0
sleep 1
if ! kill -0 $(cat $PIDFILE) >/dev/null 2>&1; then
log_failure_msg "srsd daemon failed to start"
rc=1
fi
else
rc=1
fi
if [ $rc -eq 0 ]; then
log_end_msg 0
else
log_end_msg 1
rm -f $PIDFILE
fi
} # srsd_start
case "$1" in
start)
log_daemon_msg "Starting srsd daemon" "srsd"
if [ -s $PIDFILE ] && kill -0 $(cat $PIDFILE) >/dev/null 2>&1; then
log_progress_msg "apparently already running"
log_end_msg 0
exit 0
fi
srsd_start
;;
stop)
log_daemon_msg "Stopping srsd daemon" "srsd"
start-stop-daemon --stop --quiet --oknodo --pidfile $PIDFILE
log_end_msg $?
rm -f $PIDFILE
rm -f $SOCKETFILE
;;
restart)
set +e
log_daemon_msg "Restarting srsd daemon" "srsd"
if [ -s $PIDFILE ] && kill -0 $(cat $PIDFILE) >/dev/null 2>&1; then
start-stop-daemon --stop --quiet --oknodo --pidfile $PIDFILE || true
sleep 1
else
log_warning_msg "srsd daemon not running, attempting to start."
rm -f $PIDFILE
fi
srsd_start
;;
status)
status_of_proc -p $PIDFILE "$DAEMON" srsd
exit $? # notreached due to set -e
;;
*)
echo "Usage: /etc/init.d/srsd {start|stop|restart|status}"
exit 1
esac
exit 0
Now make it executable and run at boot time.
~# chmod 755 /etc/init.d/srsd ~# update-rc.d srsd defaults
Generate a new random secret:
~# touch /etc/srsd.secret ~# chown Debian-exim /etc/srsd.secret ~# chmod 600 /etc/srsd.secret ~# openssl rand -base64 12 > /etc/srsd.secret
Start srsd:
~# service srsd start
Implement srsd integration into exim4
Create a file in /etc/exim4/conf.d/router/175_exim4-config_srs with the following content, replace spf-must-die.org to your own SRS rewriting domain:
srs_bounce:
debug_print = "R: srs_bounce for $local_part@$domain"
driver = redirect
allow_fail
allow_defer
domains = spf-must-die.org
local_part_prefix = srs0+ : srs0- : srs0= : srs1+ : srs1- : srs1=
caseful_local_part
address_data = ${readsocket{/tmp/srsd}{REVERSE $local_part_prefix$local_part@$domain}{5s}{\n}{:defer: SRS daemon failure}}
data = ${if match{$address_data}{^ERROR}{:fail: Invalid SRS address}{$address_data}}
srs_forward:
debug_print = "R: srs_forward for $local_part@$domain"
no_verify
senders = ! : ! *@+local_domains
address_data = ${readsocket{/tmp/srsd}\
{FORWARD $sender_address_local_part@$sender_address_domain spf-must-die.org\n}\
{5s}{\n}{:defer: SRS daemon failure}}
errors_to = ${quote_local_part:${local_part:$address_data}}@${domain:$address_data}
headers_add = "X-SRS: Sender address rewritten from <$sender_address> to <${quote_local_part:${local_part:$address_data}}@${domain:$address_data}> by $primary_hostname."
driver = redirect
repeat_use = false
allow_defer
data = ${quote_local_part:$local_part}@$domain
Regenerate the configuration and restart exim:
~# update-exim4.conf ~# service exim4 restart
Testing the SRS forwarding
Create an alias in /etc/aliases to your own mailbox, like this:
user: your@email.address
run newaliases to regenerate the hash table
~# newaliases
Now try to send email to user@your-mail-server.
You should get it in your mailbox.. look at the message source, you will see the following headers if DKIM and SRS are working (note the d=rewriting domain):
Return-Path: <SRS0=eCT+=EL=baanhofman.nl=wilco@spf-must-die.org>
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=spf-must-die.org; s=exim;
h=Content-Type:Subject:To:MIME-Version:From:Date:Message-ID; bh=Nh/X++v9YcgLCxTBH1lYXZg22kWTVrM8UJ+92lkoOFQ=;
b=eC+zN8okGJYoNUgllB9TUb9XDmHVIWYwFiIC+m2gcji5zlM+LIDYEz0Z6tAdZt1vUhugefB7DCLos6aiKwP/jShm2Cn4XTY4U+i0WG1wxf3L9wp8bs1bfo1oJLaI8iyNuSGnUDbQspWwJj1toXp2J1nGkV2MeagggaGr7+GLXro=;
X-SRS: Sender address rewritten from <wilco@baanhofman.nl> to <SRS0=eCT+=EL=baanhofman.nl=wilco@spf-must-die.org> by mail.bitlair.nl.
Enable SPF checking
Enabling SPF checking will break mail forwarding to your domain without SRS on domains that have a fail configured. This will likely block much legitimate e-mail, but if you want to forward to the big players, it's nearly mandatory to do..
To enable inbound SPF checking, add the following to the top of /etc/exim4/conf.d/acl/30_exim4-config_check_rcpt:
CHECK_RCPT_SPF=yes
Be careful if you have servers relaying e-mail for you (for instance because your mail server is IPv6 only and want to receive e-mail on IPv4 or as a fallback mailserver). You need to add all addresses of those servers to /etc/exim4/host_local_deny_exceptions.
Testing SPF checking
~$ telnet 2a02:2ca0:aaa::a843:657d 25 Trying 2a02:2ca0:aaa::a843:657d... Connected to 2a02:2ca0:aaa::a843:657d. Escape character is '^]'. 220 mail.bitlair.nl ESMTP Exim 4.80 Sun, 29 Mar 2015 14:37:47 +0200 EHLO mail.bitlair.nl 250-mail.bitlair.nl Hello mail.bitlair.nl [2a02:2ca0:aaa::a843:657d] 250-SIZE 52428800 250-8BITMIME 250-PIPELINING 250-STARTTLS 250 HELP MAIL FROM: <spf-test@openspf.net> 250 OK RCPT TO: <wilco@bitlair.nl> 550-[SPF] 2001:41d0:52:300::107c is not allowed to send mail from openspf.net. 550 Please see http://www.openspf.org/Why?scope=mfrom;identity=spf-test@openspf.net;ip=2001:41d0:52:300::107c
You should see a 550 reject here when there is an SPF FAIL.
More information on SPF and SRS
- https://www.assembla.com/wiki/show/file_sender/Configuring_SRS_with_Exim_(Debian_and_Ubuntu)
- https://github.com/Exim/exim/wiki/SRS
- http://www.openspf.org/SPF_Record_Syntax
Greylisting
Greylisting is bouncing all email from new senders with a temporary failure code. Implementing this helps a good deal against spammers, at the cost of having to wait for an email from a new sender.
Set up exim
To set up configuration, simply do
~# greylistd-setup-exim4 add ~# service greylistd restart
Now, if you want to skip greylisting on dnswl listed hosts, which I recommend: add the following line to the defer and deny sections about greylisting in /etc/exim4/conf.d/acl/30_exim4-config_check_rcpt:
!dnslists = list.dnswl.org
This will override your local greylistd blacklist and override greylisting for known good senders.
And regenerate the configuration and restart exim4
~# update-exim4.conf ~# service exim4 restart
Testing
~$ telnet 2a02:2ca0:aaa::a843:657d 25 Trying 2a02:2ca0:aaa::a843:657d... Connected to 2a02:2ca0:aaa::a843:657d. Escape character is '^]'. 220 mail.bitlair.nl ESMTP Exim 4.80 Sun, 15 Mar 2015 15:27:34 -0400 EHLO mail.bitlair.nl 250-mail.bitlair.nl Hello mail.bitlair.nl [2a02:2ca0:aaa::a843:657d] 250-SIZE 52428800 250-8BITMIME 250-PIPELINING 250-STARTTLS 250 HELP MAIL FROM: <wilco@bitlair.nl> 250 OK RCPT TO: <wilco@bitlair.nl> 451-2a02:2ca0:aaa::a843:657d is not yet authorized to deliver mail from 451 <wilco@bitlair.nl> to <wilco@bitlair.nl>. Please try later.
451 is the temporary failure error, this is the desired behaviour.
More information on Greylisting
DMARC
Be careful with DMARC, as DMARC with p=reject breaks your outbound e-mail even further than SPF. With p=reject, you will no longer be able to use mailing lists or mail forwarders, even those with SRS enabled. DMARC checks the 'From:' header, instead of the envelope sender of the mail, so setting DMARC policies will break all of your forwarding, and will make sure that your mail does not reach its destination. I also recommend that you reject all mail with a DMARC policy set on your mailing lists, because the bounces will cause your members to bounce off the mailing list.
Enable this if the risk of impersonation/identity fraud is greater than the risk of your outgoing emails not arriving at their destination. So, if you are paypal, a bank, linkedin, twitter or facebook.. or using this for internal mail only or to signal that nobody should be sending mail on behalf of a domain. If you do not have full control over your users
It does have useful features, like reporting, so setting a p=none can add at least some value to your mail setup.
Set up a mailbox
Create a user in whatever system you're using. If you're not using LDAP or MySQL or something, this should do:
~# useradd dmarc ~# passwd dmarc Enter new UNIX password: Retype new UNIX password: passwd: password updated successfully
When running a remote mailstore without LDAP/MySQL backend, this procedure has to be repeated on the mail store.
Publish a DMARC policy
You can add the following DMARC policy to your domain. p=none is important!
_dmarc IN TXT v=DMARC;p=none;rua=dmarc@bitlair.nl;ruf=dmarc@bitlair.nl
Doing something useful with the reports
This section is TODO. I haven't found a good tool yet.
More information on DMARC
LDAP integration
This assumes you already have an LDAP running. To set one up, please see the spacefed guide.
Schema
Load the qmail LDAP schema:
~# ldapadd -H ldapi:/// -Y EXTERNAL << EOF
dn: cn=qmail,cn=schema,cn=config
objectClass: olcSchemaConfig
cn: {4}qmail
olcAttributeTypes: {0}( 1.3.6.1.4.1.7914.1.2.1.1 NAME 'qmailUID' DESC 'UID of
the user on the mailsystem' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115
.121.1.27 SINGLE-VALUE )
olcAttributeTypes: {1}( 1.3.6.1.4.1.7914.1.2.1.2 NAME 'qmailGID' DESC 'GID of
the user on the mailsystem' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115
.121.1.27 SINGLE-VALUE )
olcAttributeTypes: {2}( 1.3.6.1.4.1.7914.1.2.1.3 NAME 'mailMessageStore' DESC
'Path to the maildir/mbox on the mail system' EQUALITY caseExactIA5Match SUBS
TR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{256} SIN
GLE-VALUE )
olcAttributeTypes: {3}( 1.3.6.1.4.1.7914.1.2.1.4 NAME 'mailAlternateAddress' D
ESC 'Secondary (alias) mailaddresses for the same user' EQUALITY caseIgnoreIA
5Match SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.
26{256} )
olcAttributeTypes: {4}( 1.3.6.1.4.1.7914.1.2.1.5 NAME 'mailQuota' DESC 'The am
ount of space the user can use until all further messages get bounced.' SYNTA
X 1.3.6.1.4.1.1466.115.121.1.44 SINGLE-VALUE )
olcAttributeTypes: {5}( 1.3.6.1.4.1.7914.1.2.1.6 NAME 'mailHost' DESC 'On whic
h qmail server the messagestore of this user is located.' EQUALITY caseIgnore
IA5Match SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.
1.26{256} SINGLE-VALUE )
olcAttributeTypes: {6}( 1.3.6.1.4.1.7914.1.2.1.7 NAME 'mailForwardingAddress'
DESC 'Address(es) to forward all incoming messages to.' EQUALITY caseIgnoreIA
5Match SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.
26{256} )
olcAttributeTypes: {7}( 1.3.6.1.4.1.7914.1.2.1.8 NAME 'deliveryProgramPath' DE
SC 'Program to execute for all incoming mails.' EQUALITY caseExactIA5Match SU
BSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{256} )
olcAttributeTypes: {8}( 1.3.6.1.4.1.7914.1.2.1.9 NAME 'qmailDotMode' DESC 'Int
erpretation of .qmail files: both, dotonly, ldaponly, ldapwithprog' EQUALITY
caseIgnoreIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{32} SINGLE-VALUE )
olcAttributeTypes: {9}( 1.3.6.1.4.1.7914.1.2.1.10 NAME 'deliveryMode' DESC 'mu
lti field entries of: nolocal, noforward, noprogram, reply' EQUALITY caseIgno
reIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{32} )
olcAttributeTypes: {10}( 1.3.6.1.4.1.7914.1.2.1.11 NAME 'mailReplyText' DESC '
A reply text for every incoming message' EQUALITY caseIgnoreMatch SUBSTR case
IgnoreSubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.15{4096} SINGLE-VALUE
)
olcAttributeTypes: {11}( 1.3.6.1.4.1.7914.1.2.1.12 NAME 'accountStatus' DESC '
The status of a user account: active, noaccess, disabled, deleted' EQUALITY c
aseIgnoreIA5Match SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 SINGLE-VALUE )
olcAttributeTypes: {12}( 1.3.6.1.4.1.7914.1.2.1.14 NAME 'qmailAccountPurge' DE
SC 'The earliest date when a mailMessageStore will be purged' EQUALITY numeri
cStringMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.36 SINGLE-VALUE )
olcAttributeTypes: {13}( 1.3.6.1.4.1.7914.1.2.1.15 NAME 'mailQuotaSize' DESC '
The size of space the user can have until further messages get bounced.' EQUA
LITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: {14}( 1.3.6.1.4.1.7914.1.2.1.16 NAME 'mailQuotaCount' DESC
'The number of messages the user can have until further messages get bounced.
' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: {15}( 1.3.6.1.4.1.7914.1.2.1.17 NAME 'mailSizeMax' DESC 'Th
e maximum size of a single messages the user accepts.' EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: {16}( 1.3.6.1.4.1.7914.1.3.1.1 NAME 'dnmember' DESC 'Group
member specified as distinguished name.' EQUALITY distinguishedNameMatch SYNT
AX 1.3.6.1.4.1.1466.115.121.1.12 )
olcAttributeTypes: {17}( 1.3.6.1.4.1.7914.1.3.1.2 NAME 'rfc822member' DESC 'Gr
oup member specified as normal rf822 email address.' EQUALITY caseIgnoreIA5Ma
tch SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{
256} )
olcAttributeTypes: {18}( 1.3.6.1.4.1.7914.1.3.1.3 NAME 'filtermember' DESC 'Gr
oup member specified as ldap search filter.' EQUALITY caseIgnoreIA5Match SUBS
TR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{512} )
olcAttributeTypes: {19}( 1.3.6.1.4.1.7914.1.3.1.4 NAME 'senderconfirm' DESC 'S
ender to Group has to answer confirmation email.' EQUALITY booleanMatch SYNTA
X 1.3.6.1.4.1.1466.115.121.1.7 SINGLE-VALUE )
olcAttributeTypes: {20}( 1.3.6.1.4.1.7914.1.3.1.5 NAME 'membersonly' DESC 'Sen
der to Group must be group member itself.' EQUALITY booleanMatch SYNTAX 1.3.6
.1.4.1.1466.115.121.1.7 SINGLE-VALUE )
olcAttributeTypes: {21}( 1.3.6.1.4.1.7914.1.3.1.6 NAME 'confirmtext' DESC 'Tex
t that will be sent with sender confirmation email.' EQUALITY caseIgnoreMatch
SUBSTR caseIgnoreSubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.15{4096}
SINGLE-VALUE )
olcAttributeTypes: {22}( 1.3.6.1.4.1.7914.1.3.1.7 NAME 'dnmoderator' DESC 'Gro
up moderator specified as Distinguished name.' EQUALITY distinguishedNameMatc
h SYNTAX 1.3.6.1.4.1.1466.115.121.1.12 )
olcAttributeTypes: {23}( 1.3.6.1.4.1.7914.1.3.1.8 NAME 'rfc822moderator' DESC
'Group moderator specified as normal rfc822 email address.' EQUALITY caseIgno
reIA5Match SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.12
1.1.26{256} )
olcAttributeTypes: {24}( 1.3.6.1.4.1.7914.1.3.1.9 NAME 'moderatortext' DESC 'T
ext that will be sent with request for moderation email.' EQUALITY caseIgnore
Match SUBSTR caseIgnoreSubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.15{4
096} SINGLE-VALUE )
olcAttributeTypes: {25}( 1.3.6.1.4.1.7914.1.3.1.10 NAME 'dnsender' DESC 'Allow
ed sender specified as distinguished name.' EQUALITY distinguishedNameMatch S
YNTAX 1.3.6.1.4.1.1466.115.121.1.12 )
olcAttributeTypes: {26}( 1.3.6.1.4.1.7914.1.3.1.11 NAME 'rfc822sender' DESC 'A
llowed sender specified as normal rf822 email address.' EQUALITY caseIgnoreIA
5Match SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.
26{256} )
olcAttributeTypes: {27}( 1.3.6.1.4.1.7914.1.3.1.12 NAME 'filtersender' DESC 'A
llowed sender specified as ldap search filter.' EQUALITY caseIgnoreIA5Match S
UBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{512}
)
olcAttributeTypes: {28}( 1.3.6.1.4.1.7914.1.4.1.1 NAME 'qladnmanager' DESC ''
EQUALITY distinguishedNameMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.12 )
olcAttributeTypes: {29}( 1.3.6.1.4.1.7914.1.4.1.2 NAME 'qlaDomainList' DESC ''
EQUALITY caseIgnoreIA5Match SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6
.1.4.1.1466.115.121.1.26{256} )
olcAttributeTypes: {30}( 1.3.6.1.4.1.7914.1.4.1.3 NAME 'qlaUidPrefix' DESC ''
EQUALITY caseIgnoreIA5Match SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.3.6.
1.4.1.1466.115.121.1.26{256} SINGLE-VALUE )
olcAttributeTypes: {31}( 1.3.6.1.4.1.7914.1.4.1.4 NAME 'qlaQmailUid' DESC '' E
QUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: {32}( 1.3.6.1.4.1.7914.1.4.1.5 NAME 'qlaQmailGid' DESC '' E
QUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: {33}( 1.3.6.1.4.1.7914.1.4.1.6 NAME 'qlaMailMStorePrefix' D
ESC '' EQUALITY caseIgnoreIA5Match SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX
1.3.6.1.4.1.1466.115.121.1.26{256} SINGLE-VALUE )
olcAttributeTypes: {34}( 1.3.6.1.4.1.7914.1.4.1.7 NAME 'qlaMailQuotaSize' DESC
'' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: {35}( 1.3.6.1.4.1.7914.1.4.1.8 NAME 'qlaMailQuotaCount' DES
C '' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE
)
olcAttributeTypes: {36}( 1.3.6.1.4.1.7914.1.4.1.9 NAME 'qlaMailSizeMax' DESC '
' EQUALITY integerMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 SINGLE-VALUE )
olcAttributeTypes: {37}( 1.3.6.1.4.1.7914.1.4.1.10 NAME 'qlaMailHostList' DESC
'' EQUALITY caseIgnoreIA5Match SUBSTR caseIgnoreIA5SubstringsMatch SYNTAX 1.
3.6.1.4.1.1466.115.121.1.26{256} )
olcObjectClasses: {0}( 1.3.6.1.4.1.7914.1.2.2.1 NAME 'qmailUser' DESC 'QMail-L
DAP User' SUP top AUXILIARY MUST mail MAY ( uid $ mailMessageStore $ homeDire
ctory $ userPassword $ mailAlternateAddress $ qmailUID $ qmailGID $ mailHost
$ mailForwardingAddress $ deliveryProgramPath $ qmailDotMode $ deliveryMode $
mailReplyText $ accountStatus $ qmailAccountPurge $ mailQuotaSize $ mailQuot
aCount $ mailSizeMax ) )
olcObjectClasses: {1}( 1.3.6.1.4.1.7914.1.3.2.1 NAME 'qmailGroup' DESC 'QMail-
LDAP Group' SUP top AUXILIARY MUST ( mail $ mailAlternateAddress $ mailMessag
eStore ) MAY ( dnmember $ rfc822member $ filtermember $ senderconfirm $ membe
rsonly $ confirmtext $ dnmoderator $ rfc822moderator $ moderatortext $ dnsend
er $ rfc822sender $ filtersender ) )
olcObjectClasses: {2}( 1.3.6.1.4.1.7914.1.4.2.1 NAME 'qldapAdmin' DESC 'QMail-
LDAP Subtree Admin' SUP top AUXILIARY MUST ( qlaDnManager $ qlaDomainList $ q
laMailMStorePrefix $ qlaMailHostList ) MAY ( qlaUidPrefix $ qlaQmailUid $ qla
QmailGid $ qlaMailQuotaSize $ qlaMailQuotaCount $ qlaMailSizeMax ) )
EOF
Exim LDAP integration
Add the following two routers:
/etc/exim4/conf.d/router/450_exim4-config_ldap_aliases:
ldap_aliases:
driver = redirect
allow_fail
allow_defer
data = ${lookup ldapm{ \
user=cn=exim,ou=System,dc=bitlair,dc=nl \
pass=That would be dumb \
ldaps://ldap.bitlair.nl/dc=bitlair,dc=nl?mailForwardingAddress?sub?\
(&\
(objectclass=qmailUser)\
(|\
(mail=${quote_ldap:$local_part}@${quote_ldap:$domain})\
(mailAlternateAddress=${quote_ldap:$local_part}@${quote_ldap:$domain})\
)\
)} {$value} fail }
file_transport = address_file
pipe_transport = address_pipe
/etc/exim4/conf.d/router/451_exim4-config_ldap_users:
ldap_users:
driver = redirect
allow_fail
allow_defer
data = ${lookup ldapm{ \
user=cn=exim,ou=System,dc=bitlair,dc=nl \
pass=Still not that dumb \
ldaps://ldap.bitlair.nl/dc=bitlair,dc=nl?uid?sub?\
(&\
(objectclass=posixAccount)\
(|\
(mail=${quote_ldap:$local_part}@${quote_ldap:$domain})\
(mailAlternateAddress=${quote_ldap:$local_part}@${quote_ldap:$domain})\
)\
)} {$value} fail }
file_transport = address_file
pipe_transport = address_pipe
/etc/exim4/conf.d/router/454_exim4-config_ldap_accept:
ldap_accept:
driver = accept
condition = ${lookup ldapm{ \
user=cn=exim,ou=System,dc=bitlair,dc=nl \
pass=!!Not this stupid!! \
ldaps://ldap.bitlair.nl/dc=bitlair,dc=nl?uid?sub?\
(&\
(objectclass=posixAccount)\
(|\
(uid=${quote_ldap:$local_part})\
)\
)} {$value} fail }
transport = lmtp
If you want wildcard domain matching for your domain add the following (Note: to use wildcards in LDAP set the attribute mail or mailAlternateAddress to @domain.tld):
/etc/exim4/conf.d/router/452_exim4-config_ldap_wildcard_aliases:
ldap_wildcard_aliases:
driver = redirect
allow_fail
allow_defer
data = ${lookup ldapm{ \
user=cn=exim,ou=System,dc=bitlair,dc=nl \
pass=!!Not this stupid!! \
ldaps://ldap.bitlair.nl/dc=bitlair,dc=nl?uid?sub?\
(&\
(objectclass=qmailUser)\
(|\
(mail=@${quote_ldap:$domain})\
(mailAlternateAddress=@${quote_ldap:$domain})\
)\
)} {$value} fail }
file_transport = address_file
pipe_transport = address_pipe
/etc/exim4/conf.d/router/453_exim4-config_ldap_wildcard_users:
ldap_wildcard_users:
driver = redirect
allow_fail
allow_defer
data = ${lookup ldapm{ \
user=cn=exim,ou=System,dc=bitlair,dc=nl \
pass=!!Not this stupid!! \
ldaps://ldap.bitlair.nl/dc=bitlair,dc=nl?uid?sub?\
(&\
(objectclass=posixAccount)\
(|\
(mail=@${quote_ldap:$domain})\
(mailAlternateAddress=@${quote_ldap:$domain})\
)\
)} {$value} fail }
file_transport = address_file
pipe_transport = address_pipe
Testing Exim LDAP integration
To run a lookup:
~# exim -bt -d+lookup wilco@bitlair.nl
To assemble to proper query:
~# exim -be
> ${lookup ldapm{ user=bla pass=bla ldaps://your.ldap.server/dc=your,dc=basedn?mail?sub?mail=wilco@bitlair.nl}}
wilco@bitlair.nl
Should give you back your email address.
Saslauthd LDAP integration
Change the mechanisms to ldap in /etc/default/saslauthd
MECHANISMS="ldap"
Write up a configuration file like this in /etc/saslauthd.conf (use your own LDAP settings):
ldap_bind_dn: cn=exim,ou=System,dc=bitlair,dc=nl ldap_bind_pw: Your password ldap_servers: ldaps://ldap.bitlair.nl/ ldap_search_base: dc=bitlair,dc=nl ldap_filter: (&(objectclass=posixAccount)(uid=%u))
Restart saslauthd.
~# service saslauthd restart
Testing saslauthd LDAP integration
~# testsaslauthd -u johndoe -p secret
Should give back something like:
0: OK "Success."
Next up is testing SASL exim, see the SASL integration section for exim, above here.
More information on LDAP integration
- https://spacefed.net/wiki/index.php/Howto/Spacenet/Setup_LDAP
- http://blog.toxa.de/archives/493
- http://www.slideshare.net/jpmens/exim-and-ldap-1829032
LMTP delivery
If you want to deliver your e-mail via LMTP, just set dc_localdelivery='lmtp' in update-exim4.conf.conf. Then follow either the local or remote delivery section of this guide. Using the remote delivery section has the advantage of allowing full disk crypto on the mail store. You cannot do this on the MTA, because it needs to power on automatically to accept new emails instantly.
Local delivery
For local delivery to dovecot, add this section in /etc/exim4/conf.d/transport/40-exim4_config-lmtp (create it if it does not exist):
lmtp:
driver = lmtp
socket = /var/run/dovecot/lmtp
#maximum number of deliveries per batch, default 1
batch_max = 200
For remote delivery with 3 week hold function via LMTP
Setting up remote delivery via LMTP makes sense, because you can have your mail store encrypted and still receive new emails, because the MTA will keep accepting mails. To set this up, update exim's retry policy for ::1, so that the MTA will hold on to temporarily failed e-mail deliveries for 3 weeks and will retry every 5 minutes.
Add the following in /etc/exim4/conf.d/retry/30_exim4-config:
::::1 * F,3w,5m
In transport/40-exim4-config-lmtp, add/modify the lmtp section to match this (create the file if it does not exist):
lmtp: driver = smtp protocol = lmtp port = 24 hosts = ::::1 allow_localhost return_path_add
This will deliver to localhost on port 24. If you want to use a mail store with full disk crypto seperate from your Mail Transfer Agent, configure a secure tunnel from local port 24 to the LDA. That's because LMTP with crypto is not supported properly by dovecot.. and exim4 does not support delivery to TLS-on-connect secure tunnels.. so.. we will configure a pair of stunnels.
Regenerate the configuration and restart exim:
~# update-exim4.conf ~# service exim4 restart
Dovecot doesn't support TLS for LMTP, so install stunnel4 using apt-get install stunnel4 on both the mailstore and the MTA machine. To properly do this, first set up a CA on the mail store with a client cert for all of your MTAs.
The easiest way to set up a CA (use a descriptive name as common name, e.g. My LMTP client CA):
~$ mkdir CA ~$ cd CA ~$ /usr/lib/ssl/misc/CA.pl -newca ~$ /usr/lib/ssl/misc/CA.pl -newreq-nodes ~$ /usr/lib/ssl/misc/CA.pl -signreq
This will result in a newcert.pem and newkey.pem which need to be transferred to the MTA in /etc/ssl/lmtpcert.pem and /etc/ssl/private/lmtpkey.pem, and in demoCA/cacert.pem is the CA you just created, copy that to /etc/ssl/lmtpca.pem.
On the MTA, create a /etc/stunnel/lmtp.conf, with the following contents:
setuid = stunnel4 setgid = stunnel4 pid = /var/run/stunnel4/lmtp.pid debug = 7 output = /var/log/stunnel4/stunnel.log verify = 2 CAfile = /etc/ssl/certs/ca-certificates.crt cert = /etc/ssl/lmtpcert.pem key = /etc/ssl/private/lmtpkey.pem options = SINGLE_ECDH_USE options = SINGLE_DH_USE [lmtp] client = yes accept = ::1:24 connect = imap.bitlair.nl:24 ; vim:ft=dosini
The other end (in this case dovecot), should have a similar stunnel4 setup. Note that the IMAP certificate is generated in the dovecot section (further down).
Create a /etc/stunnel/lmtp.conf, with the following contents:
setuid = stunnel4 setgid = stunnel4 pid = /var/run/stunnel4/lmtp.pid debug = 7 output = /var/log/stunnel4/stunnel.log cert = /etc/ssl/imap.bitlair.nl-cert.pem key = /etc/ssl/private/imap.bitlair.nl-key.pem CAfile = /etc/ssl/lmtpca.pem verify = 2 options = SINGLE_ECDH_USE options = SINGLE_DH_USE [lmtp] accept = :::24 connect = /var/run/dovecot/lmtp ; vim:ft=dosini
Now on both the MTA and the mail store, start the stunnel services.
~# service stunnel4 start
Testing LMTP delivery
To test if LMTP works, you need to have dovecot set up already. Send yourself an e-mail, see if it arrives.
More information on LMTP
- http://www.exim.org/exim-html-current/doc/html/spec_html/ch-the_lmtp_transport.html
- http://wiki2.dovecot.org/LMTP
- https://www.ietf.org/rfc/rfc2033.txt
Mailman
Mailman is a mailing list server. Setting this up will enable you to run both public and private, archived mailing lists, compatible with DKIM and SPF. Note that DMARC policies interfere with mailing lists, so either reject mail from DMARC p=reject domains or Munge the from address in the mails..
You will need a mailing list subdomain, for example list.bitlair.nl. This way, Exim will route messages through a pipe if it's destined for a mailing list.
Getting a certificate
Generate a certificate for list.your.domain and get it signed at a CA.
~# openssl req -sha256 -days 3650 -nodes -new -newkey rsa:4096 -keyout /etc/ssl/private/list.bitlair.nl-key.pem -out /etc/ssl/list.bitlair.nl-csr.pem
Input your location and contact information. At the CN field, input your mail hostname (list.bitlair.nl in my case). Do not enter a challenge password.
Submit the -csr.pem file to a CA, store the certificate you get signed from the CA in /etc/ssl/list.your.domain-cert.pem.
Setting up Mailman
First thing is to create a mailman mailing list.
~# newlist mailman Enter the email of the person running the list: your@email.address Initial mailman password:
Set the URL and mailing list domain in /etc/mailman/mm_cfg.py:
#------------------------------------------------------------- # Default domain for email addresses of newly created MLs DEFAULT_EMAIL_HOST = 'list.bitlair.nl' #------------------------------------------------------------- # Default host for web interface of newly created MLs DEFAULT_URL_HOST = 'list.bitlair.nl'
Add the following lines near the end in /etc/mailman/mm_cfg.py to streamline message sending.
# Max recipients for each message SMTP_MAX_RCPTS = 1000 # Max messages sent in each SMTP connection SMTP_MAX_SESSIONS_PER_CONNECTION = 1
Configuring Exim for mailman
Unfortunately, mailman 2.1 does not support LMTP yet. It requires a bit more configuration to get the mailman transport going. Mailman 2.2 (development branch now deprecated in favour of 3.0) does have it, so once mailman 3 arrives, upgrade to a more simple configuration set-up than this.
Configure the mailman exim settings in /etc/exim4/conf.d/main/05_exim4-config_mailman_options:
# Mailman macro definitions
# Home dir for the Mailman installation
MM_HOME=/var/lib/mailman
# User and group for Mailman
MM_UID=list
MM_GID=list
#
# Domains that your lists are in - colon separated list
# you may wish to add these into local_domains as well
domainlist mm_domains=list.bitlair.nl
# The path of the Mailman mail wrapper script
MM_WRAP=MM_HOME/mail/mailman
#
# The path of the list config file (used as a required file when
# verifying list addresses)
MM_LISTCHK=MM_HOME/lists/${lc::$local_part}/config.pck
Configure the mailman router in /etc/exim4/conf.d/router/449_exim4-config_mailman_router:
mailman_router:
driver = accept
domains = +mm_domains
require_files = MM_LISTCHK
local_part_suffix_optional
local_part_suffix = -admin : \
-bounces : -bounces+* : \
-confirm : -confirm+* : \
-join : -leave : \
-owner : -request : \
-subscribe : -unsubscribe
transport = mailman_transport
Configure the mailman transport in /etc/exim4/conf.d/transport/40_exim4-config_mailman_pipe:
mailman_transport:
driver = pipe
command = MM_WRAP \
'${if def:local_part_suffix \
{${sg{$local_part_suffix}{-(\\w+)(\\+.*)?}{\$1}}} \
{post}}' \
$local_part
current_directory = MM_HOME
home_directory = MM_HOME
user = MM_UID
group = MM_GID
Configure exim to accept mail for list.yourdomain.tld in /etc/exim4/update-exim4.conf.conf, by adding it to the dc_other_hostnames list. This is a semicolon-separated list.
dc_other_hostnames='bitlair.nl;spf-must-die.org;list.bitlair.nl'
Configuring apache for mailman
Create a site configuration in /etc/apache2/sites-available/list.bitlair.nl:
<VirtualHost *:443>
ServerName list.bitlair.nl
ServerAdmin your@email.address
DocumentRoot /var/www/
SSLEngine on
SSLCertificateFile /etc/ssl/list.bitlair.nl-cert.pem
SSLCertificateKeyFile /etc/ssl/private/list.bitlair.nl-key.pem
SSLCertificateChainFile /etc/ssl/sub.class2.server.sha2.ca.pem
SSLProtocol all -SSLv2 -SSLv3
SSLHonorCipherOrder on
SSLCipherSuite "EECDH+ECDSA+AESGCM EECDH+aRSA+AESGCM EECDH+ECDSA+SHA384 \
EECDH+ECDSA+SHA256 EECDH+aRSA+SHA384 EECDH+aRSA+SHA256 \
EECDH !aNULL !eNULL !LOW !3DES !MD5 !EXP !PSK !SRP !DSS"
<Directory /var/www/>
Options Indexes FollowSymLinks MultiViews
AllowOverride None
Order allow,deny
allow from all
# This directive allows us to have apache2's default start page
# in /apache2-default/, but still have / go to the right place
RedirectMatch ^/$ /cgi-bin/mailman/listinfo
</Directory>
ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
<Directory "/usr/lib/cgi-bin">
AllowOverride None
Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
Order allow,deny
Allow from all
</Directory>
Alias /pipermail /var/lib/mailman/archives/public
Alias /images/mailman /usr/share/images/mailman
<Directory /var/lib/mailman/archives/public>
DirectoryIndex index.html
</Directory>
</VirtualHost>
Of course, replace list.bitlair.nl with your own list subdomain.
Give permission to the web user to modify list data by adding www-data to the group list.
~# usermod -a -G list www-data
Enable the site and ssl module
~# a2enmod ssl ~# a2ensite list.bitlair.nl
Reload apache's configuration gracefully
~# apache2ctl graceful
Setting up mailing lists
TODO, guided tour:
- Set DMARC-policies!
Testing Mailman
Browse to your list url, e.g. https://list.bitlair.nl. Create a mailing list and subscribe yourself and a test mail address. Play around with the settings until you're comfortable with it.
To verify your SSL-setup on your URL:
~# openssl s_client -connect list.bitlair.nl:443 -verify 5 -CAfile /etc/ssl/certs/ca-certificates.crt
... >snip< ...
Verify return code: 0 (ok)
---
Should give you the Verify return code 0 (ok) again, any other status code means there is something wrong with your certificate.
More information about mailman
- http://wiki.list.org/DEV/DMARC
- http://www.exim.org/howto/mailman21.html
- https://www.debian-administration.org/article/617/Mailman_and_Exim4
- https://www.gnu.org/software/mailman/
Dovecot
Getting a certificate
Generate a certificate for imap.your.domain and get it signed at a CA.
~# openssl req -sha256 -days 3650 -nodes -new -newkey rsa:4096 -keyout /etc/ssl/private/imap.bitlair.nl-key.pem -out /etc/ssl/imap.bitlair.nl-csr.pem
Input your location and contact information. At the CN field, input your mail hostname (imap.bitlair.nl in my case). Do not enter a challenge password.
Submit the -csr.pem file to a CA, store the certificate you get signed from the CA in /etc/ssl/imap.your.domain-cert.pem.
Setting up dovecot
Configuring dovecot should be pretty straightforward. The first step is to disable plain IMAP.
In /etc/dovecot/conf.d/10-master.conf set port = 0 for both imap and pop3 and enable imaps. Only use the TLS-protected ports.
inet_listener imap {
port = 0
}
inet_listener imaps {
port = 993
ssl = yes
}
In /etc/dovecot/conf.d/10-ssl.conf, disable SSLv3, mandate TLS and configure your certificates:
ssl = required ssl_cert = </etc/ssl/imap.bitlair.nl-cert.pem ssl_key = </etc/dovecot/private/imap.bitlair.nl-key.pem ssl_protocols = !SSLv2 !SSLv3
Set the mail location where you want your mail delivered in /etc/dovecot/conf.d/10-mail.conf
mail_location = mdbox:/srv/mail/%n
If you want mailbox sharing between users, dovecot needs to setuid all mailboxes with the same user, so set this in /etc/dovecot/conf.d/10-mail.conf
mail_uid = vmail mail_gid = vmail
Enable the lmtp service in /etc/dovecot/conf.d/10-master.conf and override the user, so LMTP doesn't run as root.
service lmtp {
user = vmail
unix_listener lmtp {
}
}
Set the auth_username_format to %n in /etc/dovecot/conf.d/10-auth.conf, to make sure mail sent to username@domain via LMTP is delivered to the lower case username.
auth_username_format = %Ln
Set the autocreate setting properly for the Local Delivery Agent in /etc/dovecot/conf.d/15-lda.conf:
lda_mailbox_autocreate = yes
Create the vmail user and create the mail store
~# useradd --system vmail ~# mkdir -m 0700 /srv/mail ~# chown vmail: /srv/mail
To set up sieve filters, uncomment the listen section in /etc/dovecot/conf.d/20-managesieve.conf:
service managesieve-login {
inet_listener sieve {
port = 4190
}
}
Now we are going to change a few things in order to get sieve working properly.
First open and comment out the following in "/etc/dovecot/conf.d/90-sieve.conf":
# sieve = ~/.dovecot.sieve # sieve_dir = ~/sieve
the reason we need to comment out the above entries is because a users home directory for mail is "/srv/mail/%n" (%n = Username)and what the default actually says is check "/home/%n" for the sieve script which will fail due to the fact the vmail user cannot access that directory so we are going to move sieve configs to the users mailbox directory.
Now in the same file "/etc/dovecot/conf.d/90-sieve.conf" add the following just under "plugin {":
sieve = /srv/mail/%n/.dovecot.sieve
sieve_global_path = /etc/dovecot/sieve/default.sieve
sieve_dir = /srv/mail/%n
sieve_global_dir = /etc/dovecot/sieve/global/
We need to create the default directories next which will give us global rules for all users.
mkdir -p /etc/dovecot/sieve/global chown vmail:vmail -R /etc/dovecot/sieve
Now we have the directories for global rules for all users.
Now we are going to restart dovecot using the following command to update the configuration of dovecot:
## service dovecot restart
In order to test this lets add a test global rule by editing "/etc/dovecot/sieve/default.sieve" and adding the following:
require ["fileinto"];
# rule:[SPAM]
if header :contains "X-Spam-Flag" "YES" {
fileinto "Junk";
}
# rule:[SPAM2]
elsif header :matches "Subject" ["*money*","*Viagra*","Cialis"] {
fileinto "Junk";
}
now to test it send yourself a mail with money in the subject and see if it gets filed into Junk.
If it does not work try sending it from an external mailserver and see if it works then.
Now if you want to add a rule that applies only to a single user then make add the same rule to the file "/srv/mail/username/.dovecot.sieve" and make sure the file is owned and writeable by the vmail user.
that's everything you need to know about sieve if an error occurs /var/log/mail.log will tell you and a log file will be created in the same directory as the sieve rule when an issue with the rule occurs.
If you are not using LDAP then the following applies to you:
And also, if you're not going to use LDAP, set the following overrides in /etc/dovecot/conf.d/auth-system.conf.ext
userdb {
# <doc/wiki/AuthDatabase.Passwd.txt>
driver = passwd
# [blocking=no]
#args =
# Override fields from passwd
override_fields = uid=vmail gid=vmail
}
Now you're basically done. If you want LDAP integration, continue with the next section.
~# service dovecot restart
Integrating LDAP into dovecot
Make sure dovecot-ldap is installed. Change /etc/dovecot/conf.d/10-auth.conf to include auth-ldap.conf.ext and not include auth-system.conf.ext
Open /etc/dovecot/conf.d/10-auth.conf and change your overrides in the userdb section:
userdb {
driver = ldap
args = /etc/dovecot/dovecot-ldap.conf.ext
# Default fields can be used to specify defaults that LDAP may override
#default_fields = home=/home/virtual/%u
# Override fields that are always set to this value, regardless of what LDAP returns
override_fields = uid=vmail gid=vmail
}
Now open /etc/dovecot/dovecot-ldap.conf.ext, configure your exim search user, base dn and search filter.
You should be done now.
~# service dovecot restart
Testing
Testing logins:
~$ openssl s_client -connect localhost:993 * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN] Dovecot ready. 1 LOGIN username password 1 OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS MULTIAPPEND UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPECIAL-USE] Logged in 2 LOGOUT * BYE Logging out 2 OK Logout completed.
Testing your TLS configuration:
~$ openssl s_client -connect localhost:993 -CAfile /etc/ssl/certs/ca-certificates.crt -verify 5
... ->snip certificate stuff<- ...
Verify return code: 0 (ok)
---
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN] Dovecot ready.
You should see return code: 0 (ok), any other return code is bad.
To allow users to share mailboxes with each other add the following configuration changes.
Open /etc/dovecot/conf.d/10-mail.conf and uncomment the following:
namespace inbox {
type = private
separator = /
#prefix =
#location =
inbox = yes
#hidden = no
#list = yes
#subscriptions = yes
}
Make sure that following option is set in the /etc/dovecot/conf.d/10-mail.conf
protocol imap {
# Space separated list of plugins to load for all services. Plugins specific to
# IMAP, LDA, etc. are added to this list in their own .conf files.
mail_plugins = acl
}
And add the following to the end of the same file (/etc/dovecot/conf.d/10-mail.conf):
namespace {
type = shared
separator = /
prefix = shared/%%n/
location = mdbox:/srv/mail/%%n
subscriptions = yes
list = children
}
In the file /etc/dovecot/conf.d/20-imap.conf make sure the following changes are made:
protocol imap {
# Space separated list of plugins to load (default is global mail_plugins).
mail_plugins = $mail_plugins imap_acl
# Maximum number of IMAP connections allowed for a user from each IP address.
# NOTE: The username is compared case-sensitively.
#mail_max_userip_connections = 10
}
And finally add the following to the /etc/dovecot/conf.d/90-acl.conf:
plugin {
#acl = vfile:/etc/dovecot/global-acls:cache_secs=300
acl = vfile
#acl_shared_dict = file:/etc/dovecot/shared-mailboxes.db
}
# To let users LIST mailboxes shared by other users, Dovecot needs a
# shared mailbox dictionary. For example:
plugin {
#acl_shared_dict = file:/var/lib/dovecot/shared-mailboxes
acl_shared_dict = file:/srv/mail/shared-mailboxes.db
}
Hardening
Exim4 rate limiting
First, we need to make sure only 1 message is sent per connection, we also want to limit the number of simultaneous connections. For most small mail providers, allowing 20 simulataneous connections should be plenty.
Create a file in /etc/exim4/conf.d/main/04_ratelimiting with contents:
smtp_accept_max_per_connection = 1 smtp_accept_max_per_host = 1 smtp_accept_max = 20 acl_smtp_connect = acl_check_connect
And create the ACL file /etc/exim4/conf.d/acl/50_exim4-connectdelay with contents:
acl_check_connect:
accept
delay = 3s
And regenerate the configuration and restart exim4
~# update-exim4.conf ~# service exim4 restart
Testing the banner delay
~$ telnet ::1 25 Trying ::1... Connected to ::1. Escape character is '^]'. EHLO boe 554 SMTP synchronization error Connection closed by foreign host.
The SMTP banner should only appear after 3 seconds of not giving any inputs.
Rate limiting hosts with iptables
Make sure you input something like this into your firewall. The mask here implies throttling new connections for entire /64s:
ip6tables -A INPUT -p tcp --dport 25 -m state --state NEW -m recent --set --name smtpthrottle --mask ffff:ffff:ffff:ffff:: ip6tables -A INPUT -p tcp --dport 25 -m state --state NEW -m recent --update --name smtpthrottle --seconds 60 --hitcount 6 --mask ffff:ffff:ffff:ffff:: -j DROP
For legacy IP:
iptables -A INPUT -p tcp --dport 25 -m state --state NEW -m recent --set --name smtpthrottle iptables -A INPUT -p tcp --dport 25 -m state --state NEW -m recent --update --name smtpthrottle --seconds 60 --hitcount 6 -j DROP
This makes sure that nobody can connect more than 6 times per minute to your SMTP server. I also have a port scan wrapper which auto-blacklists bad people, so my firewall looks like this in my executable /etc/network/if-pre-up.d/ip6tables:
#!/bin/bash (ip6tables -F ip6tables -X ipset flush local6 ipset destroy local6 )&>/dev/null ipset create local6 hash:net hashsize 1024 family inet6 ipset add local6 2001:470:7b66::/48 ipset add local6 fe80::/16 ipset add local6 ::1/128 ip6tables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT ip6tables -A INPUT -m set --match-set local6 src -j ACCEPT ip6tables -A INPUT -p tcp -m state --state NEW -m recent --rcheck --name badpeople --seconds 3600 --hitcount 5 --mask ffff:ffff:ffff:ffff:: -j DROP ip6tables -A INPUT -p tcp --dport 25 -m state --state NEW -m recent --set --name smtpthrottle --mask ffff:ffff:ffff:ffff:: ip6tables -A INPUT -p tcp --dport 25 -m state --state NEW -m recent --update --name smtpthrottle --seconds 60 --hitcount 6 --mask ffff:ffff:ffff:ffff:: -j DROP ip6tables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --set --name sshthrottle --mask ffff:ffff:ffff:ffff:: ip6tables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --update --name sshthrottle --seconds 3600 --hitcount 5 --mask ffff:ffff:ffff:ffff:: -j DROP ip6tables -A INPUT -p tcp --dport 22 -j ACCEPT ip6tables -A INPUT -p tcp --dport 25 -j ACCEPT ip6tables -A INPUT -p icmpv6 \! --icmpv6-type redirect -j ACCEPT ip6tables -A INPUT -p tcp --dport 1:21 -m state --state NEW -m recent --set --name badpeople --mask ffff:ffff:ffff:ffff:: ip6tables -A INPUT -p tcp --dport 1:21 -m state --state NEW -m recent --update --name badpeople --seconds 3600 --hitcount 5 --mask ffff:ffff:ffff:ffff:: -j DROP ip6tables -A INPUT -p tcp --dport 26:1023 -m state --state NEW -m recent --set --name badpeople --mask ffff:ffff:ffff:ffff:: ip6tables -A INPUT -p tcp --dport 26:1023 -m state --state NEW -m recent --update --name badpeople --seconds 3600 --hitcount 5 --mask ffff:ffff:ffff:ffff:: -j DROP ip6tables -A INPUT -j DROP
More information on hardening
- http://michaelfranzl.com/2013/09/07/setting-up-exim4-mail-transfer-agent-with-spam-filtering-greylisting-and-anti-virus/
- http://techsadmin.blogspot.nl/2012/11/exim-hardening-practices.html
Troubleshooting
In general, look at the log files /var/log/exim4/mainlog and /var/log/exim4/paniclog. For Clamav, look at /var/log/clamav/clamav.log. For spamd, check out the main syslog in /var/log/syslog.
Most issues are caused by forgetting to regenerate the configuration, try regenerating and restarting exim4 to see if your problem persists.
~# update-exim4.conf ~# service exim4 restart
Forgetting to add the clamav user to the exim group
2015-03-15 14:13:46 1YXD2f-0000D2-BL malware acl condition: clamd: ClamAV returned: /var/spool/exim4/scan/1YXD2f-0000D2-BL/1YXD2f-0000D2-BL.eml: lstat() failed: Permission denied. ERROR
Can be fixed with:
~# usermod -a -G Debian-exim clamav
Not using wheezy-updates or jessie-updates repository
WARNING: Your ClamAV installation is OUTDATED! WARNING: Local version: 0.98.5 Recommended version: 0.98.6 DON'T PANIC! Read http://www.clamav.net/support/faq
Can be fixed by adding the -updates repository to /etc/apt/sources.list, for wheezy:
deb http://ftp.debian.org/debian wheezy-updates main
For Debian jessie:
deb http://ftp.debian.org/debian jessie-updates main
Forgetting to add the exim to sasl group
You'll see something like this in the mainlog:
2015-03-15 16:01:54 plain_saslauthd_server authenticator failed for (mail.bitlair.nl) [2a02:2ca0:aaa::a843:657d]:
435 Unable to authenticate at present (set_id=wilco): cannot connect to saslauthd daemon at /var/run/saslauthd/mux: Permission denied
And swaks will tell you:
<~* 435 Unable to authenticate at present
Running the following will fix it:
~# usermod -a -G sasl Debian-exim ~# service exim4 restart
auth-ldap and dovecot-ldap.conf files missing
You cannot find the auth-ldap files in the /etc/dovecot/conf.d or the dovecot-ldap file in /etc/dovecot.
Can be fixed with:
~# apt-get install dovecot-ldap
Forgetting to install dovecot-lmtpd
You've enabled the lmtp service, but when starting dovecot, the UNIX socket /var/run/dovecot/lmtp is not created.
Exim will give messages like:
2015-03-31 09:43:57 1Ycqq4-0004Q8-NP == wilco@bitlair.nl <root@bitlair.nl> R=ldap_users T=lmtp defer (-1):
Failed to connect to socket /var/run/dovecot/lmtp for lmtp transport: No such file or directory
Can be fixed with:
~# apt-get install dovecot-lmtpd
Spamassassin hits rule URIBL_BLOCKED on every mail message
You keep getting spamassassin URIBL_BLOCKED on every message.. this is likely caused by using large caching DNS servers.
Set up your own DNS server on your box to fix it.
~# apt-get install bind9
Test it with:
~$ host www.google.nl ::1
If it works, change your resolv.conf
~# echo nameserver ::1 > /etc/resolv.conf
You keep getting 550 relay not permitted for local email addresses
You most likely forgot to include your domain as a local domain.
You can change this in /etc/exim4/update-exim4.conf.conf. There is a semicolon-separated list of dc_other_hostnames. These are the hostnames to accept mail for.
After adding your domains to this file, run
~# update-exim4.conf ~# service exim4 restart
Unable to verify the first certificate
Verify return code: 21 (unable to verify the first certificate)
This means you forgot to append the chain file to the certificate. See the TLS section on appending the certificate chain and check the certificate chain you see in the s_client output.
Verify that there are two certificates in /etc/ssl/your-mailserver-cert.pem. The first one should be your mail certificate and the second one should be the chain file.
TLS not available and Error while reading file message in exim4.log
You will get output from s_client like:
139736697235088:error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol:s23_clnt.c:774:
Or "TLS is currently unavailable" when issueing the STARTTLS command in SMTP.
You'll see this message in the log:
2015-04-12 18:31:50 TLS error on connection from localhost (openssl.client.net) [127.0.0.1] (cert/key setup: cert=/etc/ssl/mail.bitlair.nl-cert.pem key=/etc/ssl/private/mail.bitlair.nl-key.pem): Error while reading file.
This can be fixed by setting the access rights appropriately (see the TLS section). Don't forget to restart exim4! The problem may also be caused by not restarting exim4 adding Debian-exim to the ssl-cert group. It may also be caused by the certificates being missing or a typo in the location in the configuration file. After editing, regenerate the configuration file!
Keep getting 421 Unexpected failure after RCPT TO
Check your exim4 mainlog, it may say something like "no host name found for IP address xxxx:xxx:xxx::xxx. Your mail server will only accept mail if you have a valid reverse DNS entry.
DKIM signatures are not added
Add some debugging output to your mainlog by setting this debug_print in /etc/exim4/conf.d/transport/30_exim4-config_remote_smtp:
remote_smtp: debug_print = "T: remote_smtp for $local_part@$domain, DKIM domain DKIM_DOMAIN DKIM_FILE"
Now, stop exim4:
~# service exim4 stop
Now, start exim4 in transport debugging mode in a new terminal:
~# exim -bd -d+transport
Now you can send yourself another email and you should see messages about which DKIM domain and key it is going to use in the debugging output