Dominic Raferd:
> My idea is to force a delay (2 seconds say) between the initial
> failure and the re-sending of the same email (same queue-id) to the
> secondary mx (or fallback relay) - in the intervening time the message
> may be pulled from the queue. Following earlier advice from Wietse
> here I am already using 'smtp_transport_rate_delay = 5s', but although
> helpful in other respects this does not delay the re-sending in this
> case.
That won't work well because the 'next mx' is chosen in the SMTP
client (i.e. the message is not returned to the queue between
attempts to deliver the message to different MX hosts) and we don't
want to pause the SMTP client as that would prevent it from delivering
other email.
(the destination rate delay is per destination and must therefore
be implemented in the queue manager).
You can reduce the number of MX hosts to try to just 1, by setting
up an SMTP client for gmail etc. that has
smtp -o smtp_mx_session_limit=1
With that, Postfix still tries multiple MX hosts until one responds,
and you will have $min_backoff-time or more to dig into the queue
and remove the offending message.
Wietse
