Backup MX, no anti-spam - you suggest don't use.
Is your advice still the same if the backup MX only backups an Imail server, has no other purpose in life, and transfers all mail only to the primary? And the primary is running anti-spam stuff.
A lot of anti-spam is based on blocking by IP sending to the MX, before the SMTP DATA command, and you lose that if you must receive from a wide-open backup MX. Being able to block at the envelope can have enormous savings in bandwidth.
Look at this, for IMGate machine in front of any IMail machine, for all of Monday's traffic:
Grand Totals ------------ messages
113754 received (this number is in fact much smaller, reporting error)
29898 delivered
56 forwarded
119 deferred (312 deferrals)
137 bounced
102045 rejected (77%) ( 102K is accurate )
0 reject warnings
0 held
0 discarded (0%)1036m bytes received 1451m bytes delivered 11149 senders 3299 sending hosts/domains 8543 recipients 1639 recipient hosts/domains
So that's 1 GB received, and probably about 3 GB rejected, per day. That's 3GB blocked from your WAN link, and 100K mgs NOT no longer recieved and scanned by the Imail box.
This new IMGate operator reports huge improvement in the operation of his Imail machine.
Scott has a way of looking at the penultimate Received: header (the one "behind" the sending MTA), which is certainly better than nothing, but it does require receiving the entire message (all the DATA).
But this is the well-known trade-off between envelope-rejecting and rejecting after content-scanning. Content-scanning is ok if you have enough power to keep up, and obviously a lot of Imail machines do.
Len
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