[GRLUG] Sendmail as secondary (backup) MX

[Benjamin Eavey]

Has anyone set this up and worked out all the kinks?  I have a machine 
running Sendmail and acting as a backup MX for several domains. 
Everything has been working fine, for the most part, but now I'm running 
into problems with the queue becoming overloaded.

It looks like a bunch of spam, and it appears to be a bunch of "550 - 
undeliverable" messages and other similar stuff.  Looks like the 
spammers are sending to non-existent addresses at the domains I host, 
which are then bouncing with "undeliverable" messages, which are then 
building up on my sendmail server, which is trying to deliver them to 
the spoofed originating email addresses.

I know this is bad, and I'm pulling my hair trying to figure out how to 
make this work properly, but I'm not getting anywhere.

Can anyone offer any suggestions?  Am I explaining this well enough that 
the problem makes sense?

Thanks,

-Ben