On 2023-05-22 at 08:36:49 UTC-0400 (Mon, 22 May 2023 14:36:49 +0200
(CEST))
Bernardo Reino via Postfix-users <rei...@bbmk.org>
is rumored to have said:
My world is only a very small subset of the real world :), but in that
world, if I say that a given server is the MX for a domain, then
that's that, it should not relay further.
No.
Historically, domains would be configured with multiple MX records
pointing to diverse machines because one could not rely on perfect
connectivity and in some cases it was actually more or less expensive
(in resources or actual money) to route mail via one or another path.
This is why MX records have a "cost" field, and it is expected that
whichever MX host one relays to, it will end up in the same mailbox.
Usually this means that higher-cost MX hosts relay messages with SMTP to
the lowest-cost MX host, but not always.
In the modern world, connectivity and individual host availability have
become good enough for most cases that it is more trouble than it is
worth to have diverse MX hosts with varied cost metrics. The use of
multiple MX records has evolved into a mechanism for load balancing and
availability in very large systems and playing standard-compliance games
with spammers ("no-listing") for smaller systems.
--
Bill Cole
b...@scconsult.com or billc...@apache.org
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Not Currently Available For Hire
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