Here is my predicament:

1. Numerous foreign emails are being sent from my server. I can provide samples.

2. If these email are originating from inside my trusted network I'm not sure how to find out how. maillog does not offer any clues that I can see.

3. I've done many online open relay scans and all say "not" an open relay.

4. I've read up on smtpauth and it sounds like something I'd like to do
but I still have questions about it. And would that patch the problem or fix it?

5. One ISP that we send a lot of emails to has already blacklisted us more than once.

Here is what I'm running:

Fedora Core 5
Sendmail 8.13
Clients using Outlook and OE

Any help would be appreciated
Thanks
Tim

Sounds to me like a client machine that uses and has authorization to send emails through this mail server has been compromised with a virus, trojan, etc. Find the originating sender and shut them down.

And if that's the real case, this should give you every argument to whoever to get rid of Outlook and OE, as these are the most targeted clients and most vulnerable.