{{tag>mail exim4}}

====== Configure exim4 to bypass local mail delivery ======

If you will be receiving email via Google mail and have a custom domain registered with them e.g. yourdomain.com, but that domain is also pointing to your server then you need to setup a hubbed host on your server to properly receive mail sent from your server at smth@yourdomain.com. The server (exim) needs to know that "smth" is not a user on the server but a email inbox at Google.

===== Make sure the router exists first =====

  cat /etc/exim4/conf.d/router/150_exim4-config_hubbed_hosts

<code>
# router/150_exim4-config_hubbed_hosts
#################################

# route specific domains manually.
#
# see exim4-config_files(5) and spec.txt chapter 20.3 through 20.7 for
# more detailed documentation.

hubbed_hosts:
  debug_print = "R: hubbed_hosts for $domain"
  driver = manualroute
  domains = "${if exists{CONFDIR/hubbed_hosts}\
                   {partial-lsearch;CONFDIR/hubbed_hosts}\
              fail}"
  same_domain_copy_routing = yes
  route_data = ${lookup{$domain}partial-lsearch{CONFDIR/hubbed_hosts}}
  transport = remote_smtp
</code>

===== Create  hubbed_hosts file =====

  vi /etc/exim4/hubbed_hosts

It should contain this:
  yourdomain.com: mx.external.com:aspmx.l.google.com

===== Then restart exim: =====

  systemctl restart exim4

===== Check the mail routing on the server =====

Before:
  root@yourdomain # exim -bt smth@yourdomain.com
  R: system_aliases for smth@yourdomain.com
  smth@yourdomain.com is undeliverable: Unrouteable address

After:
  root@yourdomain # exim -bt smth@yourdomain.com
  R: hubbed_hosts for yourdomain.com
  smth@yourdomain.com
  router = hubbed_hosts, transport = remote_smtp
  host aspmx.l.google.com      [2a00:1450:400c:c0b::1b]
  host aspmx.l.google.com      [74.125.140.27]         
  host alt1.aspmx.l.google.com [2a00:1450:4010:c0f::1b]
  host alt1.aspmx.l.google.com [108.177.14.27]         
  host alt2.aspmx.l.google.com [2404:6800:4003:c00::1a]
  host alt2.aspmx.l.google.com [74.125.200.27]         
  host aspmx2.googlemail.com   [2a00:1450:4010:c0f::1a]
  host aspmx2.googlemail.com   [108.177.14.27]         
  host aspmx3.googlemail.com   [2404:6800:4003:c00::1b]
  host aspmx3.googlemail.com   [74.125.200.26]


====== Tested on ======
  * Debian 9

====== References ======
  * manual: man exim4-config_files
  * http://www.yann.com/en/configure-exim4-to-bypass-local-delivery-on-web-server-17/04/2014.html