I upgraded Avast Free to Premium and at that point my mail client lost the ability to send or retrieve mail (SMTP error) unless the mail shield is disabled. I have multiple mail accounts configured in the Mozilla client, most MAPI but one POP. I reverted back to the free version but the problem persists.
does this help http://www.avast.com/faq.php?article=AVKB91#artTitle
I encountered the certificate problem previously, but this is something else. I went through the steps again just to be sure, but the problem persists. I get a SMTP error that a message cannot be sent for “unknown reason”. Messages cannot be retrieved either. Disable mail shield and it works fine in both directions.
try avast repair
controlpanel > ad/remove programs > avast > uninstall > repair option …wait a minute and reboot
any change ?
Went through the repair and reboot. No change.