I would like to add my own experience...
I too have the same problem, i.e., from time to time (not always
) I can see the following Avast! pop up window:
(saying: "The avast! Mail Shield encountered a probelm with the secure connection to your mail server. You may need to configure the SSL scan feature manually.
Click OK to open the Mail Shield Configuration page.")
The strange thing is that in Statistics, Mail Shield seems to work (along with the others).
In view of the advice on this thread, I followed two different approaches/procedures:
a) the procedure (by the letter) described here: http://www.avast.com/en-eu/faq.php?article=AVKB91#artTitle
Yet, the problem remained
... So, I deleted the installed Avast! certificate in Thunderbird, in "Authorities" tab, (the "Servers" tab was empty from any Avast! entry, anyway) and (since I have Avast! version: 2014.9.0.2008) I followed procedure:
b) Settings > Active Protection > I chose "Mail Shield", clicked on Settings (i.e., Mail Shield Settings) > SSL Scanning (the "Scan SSL connections" was already checked), I chose "Export Certificate" (which, in contrast to the procedure in a) produces a certificate with .der -instead of .cer- format). The exportation was successful and, I imported the new one -as described in a).
Once again, the problem persists
So, clearly it seems that there a kind of conflict between Avast! and Thunderbird, therefore, I was thinking (as a workaround, and until a final solution is found) what if someone un-checks the "Scan SSL connections" ? I mean, that still the computer is protected, is not it?
Info: Avast! 2014.9.0.2008 and Thunderbird 24.1.0 on Windows 7 Professional @ 64-bit.
Thank you in advance.