[gtaSAGE-members] Secondary MXs and Spam policies.

[Adrian Chung]

[Sent this to SAGE-members as well, but thought I'd see what people
are doing more locally]

Just wanted to collect some opinions on secondary MX use and also how
people implement spam filters:

1) Does anyone use secondary MX servers that aren't under their
operational/administrative control?  Is there any benefit these days
to doing so, or will most MTA's queue mail for an unreachable primary
for a reasonable amount of time?

2) Is it considered best practice or preference to do RBL and
extensive filtering during the MTA initial session so that mail deemed

as spam is dropped on the floor earlier rather than later, or queue
the mail and have something more thorough check it and
reject/filter/tag it later?

I'm aware that having the mail queued and then rejected means that you

may end up sending bounces to non-existent (or purposely crafted)
forged envelope sender addresses.

In the case of having secondary MXs not under your control which
simply queue and forward, you lose the ability to reject mail during
the SMTP session unless you check all Received headers against RBLs.

My personal preference at the moment is to queue mail (even at the
expense of higher resource utilization) and do more thorough checks
later, than to drop things that came from an RBL-listed server at the
front door.  Maybe I don't have enough confidence in RBLs.

--
Adrian Chung (adrian at enfusion-group dot com)
http://www.enfusion-group.com/~adrian/
GPG Fingerprint: C620 C8EA 86BA 79CC 384C E7BE A10C 353B 919D 1A17
[rogue.genosha.enfusion-group.com] up 30 days, 3:00, 9 users