====== Exim4 - Install Exim4 ======

===== Install Exim4 =====

There are various Exim4 packages available.  If you need to use ACL and other features you may need to install **exim4-daemon-heavy**.

<code bash>
apt-get install exim4-daemon-heavy
</code>


===== Configuration =====

The **README.Debian.gz** file included in the exim4 packages details Debian style configuration exhaustively.

<code bash>
zless /usr/share/doc/exim4-config/README.Debian.gz
</code>

Generally, the Debian Exim 4 packages are configured through debconf.  The install prompts for questions during package installation, and your initial Exim configuration is created from your answers. You can repeat the configuration process at any time by invoking:

<code bash>
dpkg-reconfigure exim4-config
</code>

Despite the default configuration being extended somewhat from the original upstream, chances are that you'll need to manually change the Exim configuration with an editor if you intend to do something that is not covered by the debconf-driven configuration. It has never been the packages' intention to offer all possible configuration methods through debconf.

There are three ways you can configure exim4.  The first is a single monolithic file, the second is split file, and the third is your own file.

The configuration file is generated from these config files using the command (yes it has .conf in the name)

<code bash>
update-exim4.conf
</code>

After which you should restart exim4 with something like

<code bash>
service exim4 restart
</code>


==== Single Exim4 configuration file ====

If you select this option in debconf, configuration will be generated from the /etc/exim4/exim4.conf.template file.

The default file is rich with features which can be enabled and controlled merely by setting the values of various macros.

Incidentally, the /etc/exim4/exim4.conf.localmacros file will be read in first, which makes it the ideal place to put any macros you may want to set. Using this file you can control various features (DKIM for example) and still gain the benefits of not touching the debian provided files, so hopefully having more seamless upgrades.


==== Split file ====

In this scenarios the configuration is split across lots of smaller files stored in /etc/exim4/conf.d/ which are then assembled in to one file for you by the update-exim4.conf command.  Each section of the configuration file has its own subdirectory and the files therein are concatenated in alphabetical order.  As such its probably a good idea that your custom files be named something like 00_exim4-my-config so they are included first.

This mode of operation allows for your own sections of configuration to be inserted at any location in the final config file, without touching any of the package provided files. The idea being that upgrades become very reliable.


==== Your own file ====

Simply install your own file in /etc/exim/exim4.conf and exim will use that file verbatim.

To have something to start with, you can either take /etc/exim4/exim4.conf.template, run update-exim4.conf --keepcomments --output /etc/exim4/exim4.conf, or use upstream's default configuration file that is installed as /usr/share/doc/exim4-base/examples/example.conf.gz.

You are going to lose all magic you get from packaging though, so you need to be familiar with Exim to build an actually working config.

Note that /etc/exim4/exim4.conf is read directly by exim4 every time exim forks.  So if you edit it in place, each smtp connection will actually read a different configuration file!


==== Location of the auto-generated config ====

For reference, the file generated by update-exim4.conf is /var/lib/exim4/config.autogenerated

**IMPORTANT**:  Avoid editing this file in place!


==== Example stand-alone example ====

This configuration has been tested on a server and ought to be suitable for internal use:

<code bash>
dpkg-reconfigure exim4-config
</code>

Shows

<code>
General type of mail configuration:  internet site; mail is sent and received directly using SMTP.
System mail name: yourdomain.com
IP-addresses to listen on for incomming SMTP connections: // leave blank
Other destinations for which mail is accepted: yourdomain.com
Domains to relay mail for: // leave blank
Machines to relay mail for: // leave blank
Keep number of DNS-queries minimal (Dial-on-Demand) ?: No
Delivery method for local mail: Maildir format in home directory
Split configuration into small files ? : No
</code>

This writes the configuration to /etc/exim4/update-exim4.conf.conf.


===== Things you might want to configure =====

==== TLS and authentication ====

Generate a certificate using:

<code bash>
bash /usr/share/doc/exim4-base/examples/exim-gencert
</code>

It will generate exim.crt and exim.key in /etc/exim4/

Instead of generating a certificate, you may simply copy certificates that you have purchased or generated previously.

Edit /etc/exim4/exim4.conf.template

add the following line before .ifdef MAIN_TLS_ENABLE

<file bash /etc/exim4/exim4.conf.template>
MAIN_TLS_ENABLE = yes
</file>

Now restart exim.


==== SPF filtering ====

This is provided via the macro CHECK_RCPT_SPF, set it to true.

Exim uses a helper tool, which you will need to install...

<code bash>
 apt-get install spf-tools-perl
</code>

You should then run update-exim4.conf and restart exim.


==== Email sub-addressing (plus-signs as in Gmail) ====

These can easily be achieved by adding something similar to the following in one of more of your router definitions

<file bash /etc/exim4/exim4.conf.template>
local_part_suffix = +* : -* : _*
local_part_suffix_optional
</file>

The above example would deliver user+example@domain.com, user-example@domain.com and user_example@domain.com to user@domain.com.

Similarly, you could use a prefix instead with these similarly named options

<file bash /etc/exim4/exim4.conf.template>
local_part_prefix = *+ : *- : *_
local_part_prefix_optional
</file>

The above example would deliver example+user@domain.com, example-user@domain.com and example_user@domain.com to user@domain.com.

In either case, you could then use sieve filtering, config tricks or your email client to apply delivery rules.


==== Install diagnostic tools ====

<code bash>
apt-get install swaks libnet-ssleay-perl
</code>

Test the connection:

<code bash>
swaks -a -tls -q HELO -s localhost -au your_user -ap '<>'
</code>

Result

<code>
 === Trying localhost:25...
 === Connected to localhost.
 <-  220 debianwb ESMTP Exim 4.76 Thu, 04 Aug 2011 14:22:02 +0600
  -> EHLO debianwb
 <-  250-debianwb Hello localhost [127.0.0.1]
 <-  250-SIZE 52428800
 <-  250-PIPELINING
 <-  250-STARTTLS
 <-  250 HELP
  -> STARTTLS
 <-  220 TLS go ahead
 === TLS started w/ cipher DHE-RSA-AES256-SHA
  ~> EHLO debianwb
 <~  250-debianwb Hello localhost [127.0.0.1]
 <~  250-SIZE 52428800
 <~  250-PIPELINING
 <~  250 HELP
  ~> QUIT
 <~  221 evie closing connection
</code>

Note that above we are sending an empty password while testing with the swaks tool.

Some ISPs may block connecting to port 25, and also some broken clients insist TLS on Port 465.

To support these, change /etc/default/exim4 as:

<file bash /etc/default/exim4>
SMTPLISTENEROPTIONS='-oX 465:25 -oP /var/run/exim4/exim.pid'
</file>

Also edit /etc/exim4/exim4.conf.template:

<file bash /etc/exim4/exim4.conf.template> 
#####################################################
### main/03_exim4-config_tlsoptions
#####################################################
tls_on_connect_ports=465
### main/03_exim4-config_tlsoptions
#################################
</file>

Check [[http://pkg-exim4.alioth.debian.org/README/README.Debian.html#TLS|pkg-exim4.alioth.debian.org]] README for details.


==== User authentication ====

Adding user authentication is possible using tools like [[https://wiki.debian.org/Dovecot|Dovecot]] or sasl2-bin.  For shell users who would like to use SASL and PAM for password authentication, that can setup this way:

<code bash>
apt-get install sasl2-bin
</code>

Edit /etc/default/saslauthd to enable saslauth:

<file bash /etc/default/saslauthd>
START=yes
</file>

Start the deamon:

<code bash>
/etc/init.d/saslauthd start
</code>

In /etc/exim4/exim4.conf.template, uncomment the following lines to enable authentication via saslauthd:

<file bash /etc/exim4/exim4.conf.template>
 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
</file>
    
Add exim to the sasl group:

<code bash>
adduser Debian-exim sasl
</code>

Restart exim:

<code bash>
/etc/init.d/exim4 restart
</code>

Test the connection using your username:

<code bash>
swaks -a -tls -q AUTH -s localhost -au your_user
Password:
</code>

Enable IMAP access by installing [[https://wiki.debian.org/Courier-Imap|Courier-Imap]] or a similar MTA.


==== Spam scanning ====

There are several ways to detect spam.

Exim has default configuration for spamassassin (exim4-daemon-heavy required).

<code bash>
apt-get install spamassassin
</code>

If you are using Debian Jessie or later (with systemd enabled by default), enable and start the service using systemctl;


<code bash>
systemctl enable spamassassin.service
</code>

On earlier Debian releases, edit /etc/default/spamassassin ...

<file bash /etc/default/spamassassin>
ENABLED=1
</file>

...and then start the daemon.

<code bash>
/etc/init.d/spamassassin start
</code>

On all systems, edit /etc/exim4/exim4.conf.template as required for your system.

First, if necessary, set the spamd_address:

<file bash /etc/exim4/exim4.conf.template>
# For spam scanning, there is a similar option that defines the interface to
# SpamAssassin. You do not need to set this if you are using the default, which
# is shown in this commented example. As for virus scanning, you must also
# modify the acl_check_data access control list to enable spam scanning.

# spamd_address = 127.0.0.1 783
</file>

Next, edit the acl_check_data section to add suitable spam headers:

<file bash /etc/exim4/exim4.conf.template>
### acl/40_exim4-config_check_data
#################################

# This ACL is used after the contents of a message have been received. This
# is the ACL in which you can test a message's headers or body, and in
# particular, this is where you can invoke external virus or spam scanners.

acl_check_data:
...
...
...
# See the exim docs and the exim wiki for more suitable examples.
#
# 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

# put headers in all messages (no matter if spam or not)
 warn  spam = nobody:true
     add_header = X-Spam-Score: $spam_score ($spam_bar)
     add_header = X-Spam-Report: $spam_report

# add second subject line with *SPAM* marker when message
# is over threshold
  warn  spam = nobody
      add_header = Subject: ***SPAM (score:$spam_score)*** $h_Subject:
</file>
      
For more information about configuring spam filters, see the [[http://www.exim.org/exim-html-current/doc/html/spec_html/ch44.html|exim wiki]].

To test your spamassassin setup follow spamassassin [[http://spamassassin.apache.org/tests.html|test]] and [[http://spamassassin.apache.org/gtube/|gtube]].


==== Exim access control lists (ACLs) ====

Exim provides flexible way to set access control list. For detailed information, see the ACL documentation on the exim wiki.

For example, if we are trying to deny all mail from three free email service providers (domain1.com, domain2.com, domain3.com) based on Received headers from the servers, we can use the following lines:

<file bash /etc/exim4/exim4.conf.template>
deny
     condition = ${if match{$h_Received:}{\N\.(domain1|domain2|domain3)\.com\N}{yes}{no}}
     message = This mailbox does not support free e-mail services.
</file>


===== References =====


https://wiki.debian.org/Exim