Drivers were not the answer...

Also tried refreshing the DNS and turning off Semantic email scanning.  One of these two did the trick.  I'm leaning toward turning off Semantic as the answer - even though SEP was disabled as soon as the server started having issues.

Mercury 4.7 on a Windows XP professional/service pack 3

The computer originally had Novell installed.  On Friday I uninstalled Novell (weren't using it any more) and let Windows update re-start the machine.  Since then, Mercury has twice stopped functioning properly.  The program continues to accept incoming mail, but will not always connect to the users (so mail cannot be retrieved from mailboxes) and is unable to resolve MX records - so all outgoing mail sits in the queue.

Re-starting the machine clears the problem up - for a time.  But daily re-starts are not feasible.  

 the only issues found in the System error log are 'side by side' error/Generate Activation Context failed for C:\windows\system32\c. and VC90.crt cannot be found. (these happened about the same time Mercury stops working, but could be coincidental)

 ISP and web host  both claim there were no server issues on their ends which may have caused internet interruption.

 Any idea why Mercury is having issues?

I would try installing updated drivers for the network adapter (or re-installing the current drivers if they are the most recent). And as always, make sure that Mercury directories aren't monitored by any real-time antivirus software.

/Rolf