# Reject messages on backup mail exchangers when primary MX is online
On today's Internet, are backup MXes still useful? Any decent mail
client should retry for at least a couple of days, and it's been a
very long time since my main MX was down for longer than that.
For many the question isn't how long it retries, but how often. A host with
intermittent connectivity problems may want to use a secondary MX to
in effect lower the retry interval.
For a busy mail system, multiple mail hosts at the same priority make
plenty of sense, but a backup that accepts the mail, then redelivers
it to one of the main hosts later? Really?
I'm not exactly a big operation, and I operate two of them. So: Yes. Really.
Ned
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