[CentOS] spam control

Wed Oct 25 19:56:20 UTC 2006
Alex Palenschat <alex at nssmgmt.com>

John Hinton wrote:
> I don't think my users would be too happy with greylisting, unless it 
> was done only on blocklist, as they have come to enjoy the immediate 
> delivery of email. Also, greylisting has the potential of 
> hurting other 
> ISPs, clogging their systems, just because they signed up a 
> few 'stupid 
> users' who got the latest virus/trojan. If you think back to 
> some of the 
> more successful viruses, mailservers everywhere suffered with many 
> choking and going down. Adding to their mail queues isn't so nice.

While I have had a couple of mailservers that were sending legitimate
mail complain about this (greylisting all mail), the vast majority have
had no problem with it. I use the postgrey script (has it's own yum repo
too :) and after a 5 minute delay the first time a triplet
(client/sender/recipient) is seen it is auto-whitelisted. And the
greylisting happens after all sanity checks and rbls. Vastly reduced
spam from spambots which tend to just blast the mail out with no concern
for the response. But I only have 200+ mailboxes and around 15-20k
emails a day, so YMMV.
I think the bottom line is that you have to pick your MTA/Content filter
and then get on the mailing list and pay attention. It's an on-going war
and there is no set-it and forget-it.