just a tip: don't put your entire address name in the "authentication" box (no secure authentication, leave this unchecked), just your Google username, ie not peter@gmail.com, but just peter. And use 587 rather than 25 in Thunderbird SMTP (sending), and as said ssl disabled. Then check in avast mail scanner expert settings, ssl account tabs, that your account has been correctly detected, you should have two lines, one for POP redirecting to 995, ssl on, and the other one for SMTP to 587, TLS on (or 465/SSL).