Debian : configure an send-only smtp server (exim or postfix)

Please use example.com instead of domain2.com, example.com (and .org .net) was specifically created for examples and documentation.

In your /etc/exim4/update-exim4.conf.conf you have configured:

dc_use_split_config='false'

However you are changing something in /etc/exim4/conf.d/router/999_exim4-config_redirect which will be ignored because you are not using split configuration.

Either do:

dc_use_split_config='true'

And reload exim4, you may prefer to change it using:

dpkg-reconfigure exim4-config

Or edit /etc/exim4/exim4.conf.template to add your customisations instead and reload exim4 once done.

Debian exim4 has a feature called hubbed_hosts which can be a convenient way to accomplish what you want without having to add your own routers et al.

So if your want your server to send email destined for domain example.org to domain example.com which has MTAs listening on IPs 192.0.2.1 and 192.0.2.10 you do the following:

• Create /etc/exim4/hubbed_hosts and add:

  example.org: 192.0.2.1:192.0.2.10

• reload exim4

Note, no spaces between the IP addresses and they're separated by a colon ':'

What this does is it will relay email destined for example.org to IPs 192.0.2.1,192.0.2.10 (in my example the IPs of example.com). It therefore will ignore the MX records of that domain. The IP address could be anything, as long as it is configured to receive those emails.

Finally there is address rewriting, see: http://www.exim.org/exim-html-current/doc/html/spec_html/ch31.html Perhaps it has something that will fit your requirements. You could use it in addition to hubbed_hosts.

If you literally put "localhost" in that setting, try putting instead:

dc_local_interfaces='127.0.0.1 ; ::1'

During dpkg-reconfigure exim4-config, if you select *Internet site" for the type, the second question looks like this:

Please enter a semicolon-separated list of IP addresses. The Exim SMTP listener
daemon will listen on all IP addresses listed here.

An empty value will cause Exim to listen for connections on all available network
interfaces.

If this system only receives mail directly from local services (and not from other
hosts), it is suggested to prohibit external connections to the local Exim daemon.
Such services include e-mail programs (MUAs) which talk to localhost only as well
as fetchmail. External connections are impossible when 127.0.0.1 is entered here,
as this will disable listening on public network interfaces.

IP-addresses to listen on for incoming SMTP connections:

Simply put the following in that field:

127.0.0.1; ::1