Is someone spamming through me?

[Jody Cleveland]

Hello,

> You sure they are actually from your server and not someone 
> else's server
> bouncing back invalid email addresses to the alleged sender 
> in a joe-job
> style thing.

How do I check if that's the case? I looked at the maillog, and see a
lot of these:

Apr 23 08:25:50 mystique postfix/qmgr[2324]: 964A8839FDA:
to=<heberson at zipmail.com.br>, relay=none, delay=104247, status=deferred
(delivery temporarily suspended: connect to
smtp.zipmail.com.br[200.221.11.147]: server dropped connection without
sending the initial SMTP greeting)

- jody