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exim all mail catcher

All mail catcher with Exim 4, on Debian 8

We have un bunch of "development" VM that has the feature of sending a mail via a relay, or MTA. 

We usually achieve this by setting the "mail host" setting in the used framework or CMS.

But for development purpose, there is no need to really send the message over the Internet: if the "mail host" catches it all and delivers it to a mailbox, the work is done.

Here is how to setup an Exim 4 on Debian 8 in order to make it catched all mail for all destination and always deliver it to a single local mailbox. That signel local mailbox can then be accessed via IMAP so that the development team can check if the message has been sent by the application.

Configuring with "debconf"

The first stage of configuration is done with debconf

# dpkg-reconfigure exim4-config

Then choose the following answers:

  • Internet site; mail is sent and received directly using SMTP
  • System mail name: (put the FQDN of this machine)
  • IP-addresses to listen on : (leave empty)
  • Other destinations for which mail is accepted:   *
    (Remember we want to catch all destination)
  • Domains to relay mail for: *
    (Remember we want to catch all destination)
  • Machines to relay mail for: 192.168.128.0/23
    (Ajust to your subnet)
  • Keep number of DNS-queries minimal (Dial-on-Demand)? <yes>
    (As far as we wont deliver to the outside world, we dont need to query DNS)
  • The remaining options are up to you

Modify the "deconf'd" configuration

The generated configuration is stored in
/var/lib/exim4/config.autogenerated

We need to copy this to
/etc/exim4/exim4.conf

Then we edit it, and the only line to edit is in the "system_aliases:" router:
-  data = ${lookup{$local_part}lsearch{/etc/aliases}}
+  data = mihamina

This will route all the messages to the "mihamina" Maildir: just install a Dovecot-IMAP and a webmail in order to see the messages.

Note that
  • "mihamina" user must have been created.
  • we dont need to touch the "aliases" file

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