> On Jan 14, 2018, at 8:53 AM, lutz.niede...@gmx.net wrote:
>
> we are using two external MX servers in separate data centers. Both of them
> are running postfix since many years without problems.
>
> Internally we do have a postfix server as final destination for all domains.
> On each MX we have defined a relay_transport with specific settings that
> relay mail to our internal server. For this we use transport:[A RECORD]:port
> as relay_transport.
>
> Now we have two links to our internal server and we observed that it was the
> right decision to have those two links. Our internal server got two IP
> addresses (one per link) and is listening on both of them for connections
> from the MX servers. But we have no clue how to set up a secondary
> relay_transport that kicks in if the primary is offline. So, currently we
> cannot use the backup link for incoming mails. We can only specify one
> relay_transport entry, means one IP address, with a transport.
Replace the IP address with a hostname:
main.cf:
indexed = ${default_database_type}:${config_directory}/
transport_maps = ${indexed}transport
relay_host_lookup = dns, native
transport:
example.com relay:[internal.example.com]
master.cf:
relay unix ... smtp
-o smtp_host_lookup=$relay_host_lookup
/etc/hosts
# See http://www.linfo.org/etc_host_conf.html
192.0.2.1 internal.example.com
192.0.2.2 internal.example.com
This will deliver mail via either address chosen uniformly randomly.
If you need a fallback use MX records:
main.cf:
indexed = ${default_database_type}:${config_directory}/
transport_maps = ${indexed}transport
transport:
example.com relay:example.com.localhost
and configure the local DNS resolver to return MX records for
example.com.localhost:
; localhost private zone
localhost. IN A 127.0.0.1
example.com.localhost. IN MX 10 relay1.example.com.localhost.
example.com.localhost. IN MX 20 relay2.example.com.localhost.
relay1.example.com.localhost. IN A 192.0.2.1
relay2.example.com.localhost. IN A 192.0.2.2
--
Viktor.
