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Postfix transport map with failover entries?

Déjà vu

4/27/23, 7:07 AM

Postfix relays a few domains to a fixed IP address, or its failover address.

1.2.3.4 and 11.12.13.14 (failover)

These two IP addresses are where the relay should occur.

Currently, transport_map

exemple1.com   relay:[1.2.3.4]:587
exemple2.com   relay:[1.2.3.4]:587

Is there a way, in case [1.2.3.4] times out, to use the failover automatically, like

exemple1.com   relay:[1.2.3.4]:587
exemple2.com   relay:[1.2.3.4]:587
exemple1.com   relay:[11.12.13.14]:587
exemple2.com   relay:[11.12.13.14]:587

Would that work?

(There is this question which is a tad different. Adding multiple IPs to /etc/hosts (or DNS if that was possible) would use either IP. In my case the failover should only be used if the main one times out)

242

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relay

Nikita Kipriyanov

4/27/23, 7:37 AM

The [`transport (5) man page`](http://www.postfix.org/transport.5.html) says: *In the сase of the Postfix SMTP/LMTP client, the nexthop field may contain a list of nexthop destinations separated by comma or whitespace (Postfix 3.5 and later).* No further explanation is given about interpretation of such token. Probably it's worth asking in the Postfix users mailing list.

Déjà vu

4/27/23, 7:47 AM

Great, thanks. We're on Postfix 3.3 (Ubuntu 18.04 LTS) though.

csx4

9/1/24, 6:29 PM

so did it work ? how did you write like this ? exemple1.com relay:[1.2.3.4]:587,relay:[11.12.13.14]:587 exemple2.com relay:[1.2.3.4]:587,relay:[11.12.13.14]:587

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Server

AlexD

4/27/23, 7:57 AM

Excerpt from Postfix 3.5 release notes

[Feature 20200111] the Postfix SMTP and LMTP client support a list of nexthop destinations separated by comma or whitespace. These destinations will be tried in the specified order.

The list form can be specified in relayhost, transport_maps, default_transport, and sender_dependent_default_transport_maps.

Examples:

/etc/postfix/main.cf:
    relayhost = foo.example, bar.example
    default_transport = smtp:foo.example, bar.example.

NOTE: this is an SMTP and LMTP client feature. It does not work for other Postfix delivery agents.

If you don't have Postfix 3.5 you can specify the destination as a domain name without brakets - postfix will do MX lookups for that domain name and use MX to send the email.

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Déjà vu

4/27/23, 8:44 AM

Will this work with the `relay:` prefix in transport (syntax in the question). Like `exemple1.com relay:myMxDnsEntriesHost:587` ? If yes, that's a great idea, as MX includes priorities!