I’m interested in finding out if you get any responses to this.

I’ve just updated my Avast installation, and am now having issues sending email (and, occasionally, surfing the internet).

Try turning the “Webshield” off, and then sending email. That’s been working for me (it also resolved any issues I had surfing web pages).

Apparently, this has been a long-standing issue with Webshield (I’ve found references to it going back past 2010). None of the “solutions” I’ve found have fixed my issue, though (adding Avast to the firewall allow rules, adding my mail server to the exclusion list on the Webshield rules, etc).

Cheers,
…rob