Re[2]: Spammers Target Secondary MX hosts?

[Henri van Riel <sp...@vanriel.xs4all.nl>]

> The theory is probably that they can pump spam through faster if
> they utilize all an ISP's inbound MX machines :)

The theory is that most ISP don't run spam filters on their secondary
MX's because "all" smtp clients will hit the primary first and that
"always" works. The secondaries are only for backup, just in case.
Spammers seem to know that...

I had the same problem once. Someone thought it would be nice to
randomly generate several thousands of fake email address for my
sub-domain and put it on a cd to sell to spammers. Most of the spam I
received was delivered to a secondary MX of my ISP's mail cluster, all
spam delivered to the primary got filtered out by my ISP. At some point
I got 15,000 spam mails per day! I pointed out to my ISP that spammers
were using the secondary MX's for spamming and they then removed the
secondaries from my sub-domain. Now I only accept mail from the
primary MX which has a robust spam filter.

-- 
Best regards,
 Henri                            mailto:spamassassin@vanriel.xs4all.nl