Mail spam suddenly

Question

Running 10.7.5,  I have mail setup it has been working great for months.  In the last week though I have started getting tons of spam in the following format.
From: Mail Delivery System
To: My email address on the server
Subject: Undelivered Mail Returned to Sender
Body:  Is basically my mail server telling me I sent something to a user but I never did.
To verify this I checked my smtp logs and I can see that nothing went out of my mail server,  but I can see all the undeliverables pouring into my system and the end result is tons and tons of junk mail in my inbox.
Does anyone have any ideas on how I might fight this spam? 
Thanks for all the help guys!

Answer 1

Does anyone have any ideas on how I might fight this spam?
Grab yourself a beer and go sit by the pool. That's about all you can do.
If the mail isn't going through your server, you have zero influence or opportunity to affect it. The likelyhood is that someone's just generating span using a random/dummy email address that happens to map back to you.
SMTP was never really designed to authenticate mail and while you can lock down your own server there is very little you can do to prevent others generating mail (spam) in your name.
If you're really interested, look at implementing SPF and/or DomainKeys. These add a layer of authentication to your messages that can elevate the trust of your real emails, but there's no guarantee that any remote mail server will honor them, or reject mail that comes from an invalid address (SPF) or isn't properly signed (DomainKeys).
I suppose as a good domain owner you should be implementing SPF and DomainKeys anyway, since these systems are only really effective when used by the majority, but it's not going to be a golden arrow that magically makes this problem go away, hence the beer.