I've reported similar but not quite the same issues here with releases over time.
Try:
Ping your SMTP server and get the IP address. Then replace the hostname in our email config with the IP address.
My problem is usually that DNS resolution gets cutoff, but apps like Skype still work because they use an IP.
If this IS the problem, the pattern here is this:
- Avast doesn't acknowledge the issue in the forum.
- I cite a bunch of current and past examples of the exact same problem.
- They delete my posts as over-posting rather than recognizing that I'm putting multiple confirmations of an ongoing issue.
- I leave protection off.
- Within some number of days a new build is released that fixes the problem.
- We all move on like it didn't happen.
I hope you have the same luck in this area that I've had.