On 2020-12-18 05:21:51 (+0800), John Levine via mailop wrote:
As we all know, MX records have a priority number, and mail senders
are supposed to try the highest priority/lowest number servers first,
then fall back to the lower priority.
I understand why secondary MX made sense in the 1980s, when the net
was flakier, there was a lot of dialup, and there were hosts that only
connected for a few hours or even a few minutes a day.
But now, in 2020, is there a point to secondary servers? Mail servers
are online all the time, and if they fail for a few minutes or hours,
the client servers will queue and retry when they come back.
Secondary servers are a famous source of spam leaks, since they
generally don't know the set of valid mailboxes and often don't keep
their filtering in sync? What purpose do they serve now?
R's,
John
PS: I understand the point of multiple MX with the same priority for
load balancing. The question is what's the point of a high priorty
server that's always up, and a lower priority server that's, I dunno,
probably always up, too.
I use the secondary MX as spammerbait... If a client connects to a
lower priority MX before talking to the higher priority MX, I probably
don't want to hear from them.
A couple of people have suggested real-world reliability benefits to
secondary MX servers in 2020 but I see the number of those use cases
dwindling.
Not only are your servers usually up, the people sending you mail can
probably queue for a while when you're down and retry when you're back
up. This was more of a problem decades ago, when disks were small and
making queueing the sender's problem was less likely to actually work.
Philip
--
Philip Paeps
Senior Reality Engineer
Alternative Enterprises
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