On Wed, Mar 11, 2026 at 07:43:41AM -0700, list_postfix--- via Postfix-users 
wrote:

> My current config has the MTA relaying to multiple mailbox servers using
> transport_maps with entries like:
> 
> example.com foo:[a.example.com]
> example.net foo:[a.example.com]
> example.org bar:[b.example.com]
> 
> It works fine.  I get per-domain delivery routing and can use
> defer_transports to pause delivery on a per-server basis.  But it's
> annoying and a bit error prone having the nexthop specified repeatedly
> in transport_maps.

Your internal DNS can publish appropriate MX records for these domains.
As for defer_transports, if you want to pause delivery for just a single
domain, change the transort entry to "defer:delivery paused" (don't
forget to change it back promptly).

> I'd rather specify it once for each transport.  Those are delivery
> smtp clients, so it's too late to use relayhost.  But I did find the
> best_mx_transport option:
> 
> In master.cf:
> 
> testrelay unix - - n - - smtp
>   -o best_mx_transport=testrelay:[chombo.houseloki.net]:587
>   -o smtp_fallback_relay=
>   -o syslog_name=postfix/$service_name

This is not a good idea.  Just specify the transport correctly.

> 
> postfix/testrelay/smtp[41199]: C3F34112532: passing
> <[email protected]> to transport=testrelay
> postfix/testrelay/smtp[41201]: Untrusted TLS connection established to
> chombo.houseloki.net[65.100.43.2]:587: TLSv1.3 with cipher
> TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature
> RSA-PSS (4096 bits) server-digest SHA256

This required two delivery agent processes to handle the same message,
you're far better off not doing this.

> But that feels like a hack.

It is, don't do it.

> Is there a better way to do this that isn't what I already have?

Specify the correct nexthop in the transport table, or deploy MX records
in your DNS.

-- 
    Viktor.  🇺🇦 Слава Україні!
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