Hey again qasic,
The errors are documented in

this thread.

They started for me (or at least I first became aware of it) right after upgrading to 6.1.0.3. I know it was working shortly before as I sent email to all my members notifying them of the upgrade. Now, no matter what I try (IP address, alternate SMTP boxes, etc..) I am unable to get UBB to send anything out. My hosting provider (Interland) IS able to send mail from my server though. The message looks like a configuration error in UBB, but if it is, its a VERY subtle one.

I think the key here is that NOTHING changed except the upgrade to 6.1.0.3, and others are getting the exact same errors.

Any ideas?