On Tue, Jan 02, 2024 at 11:12:28AM +0100, Peter Wienemann via Postfix-users
wrote:
> To avoid a potential misunderstanding: I do not see any reason to cast doubt
> on the RFC compliance of Postfix. I think the issue discussed in this thread
> rather goes beyond what is specified in RFCs. It basically boils down to the
> question whether the RFC imposed ranking based on DNS record types is
> stronger or weaker than the ranking imposed by the order of the specified
> relay hosts. I neither found an answer to that question in RFCs nor in the
> Postfix documentation (I hope I have not missed anything). Wietse kindly
> answered that the RFC imposed ranking is implemented on the level of
> individual entries of the relay host list rather than on the ensemble of
> relay host entries. Maybe it is worth clarifying this point in the Postfix
> documentation.
FWIW, it seems clear to me that Postfix should try each destination in
turn, with all subsequent destinations as *fallback*, rather than
concurrent alteratives. For concurrent alternatives, one would define a
single destination with suitable priority MX records.
One important use case is to shunt mail that fails the first delivery
attempt to a fallback queue that processes "problem" mail.
That said, indeed the documentation is not explicit on this point, one
has to read "between the lines". If your technical writing skills are
adequate, perhaps you could suggest some concise and clear text
explaining the semantics.
This would need to be added to smtp(8), transport(5) and postconf(5),
with multiple affected parameters in the last case.
--
Viktor.
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