Good day to you lukas. I have been looking forward to having someone from the avast! team to drop in.

My mail program is Postbox 3.08
https://www.google.com/search?source=ig&rlz=&q=download+postbox&oq=download+postbox&gs_l=igoogle.1.0.0l7j0i22i30l3.354.6527.0.9365.15.11.0.4.4.0.273.1597.0j10j1.11.0...0.0...1ac.1.12.igoogle.JxlLOb9w-Zc

It is very similar to Thunderbird.

My friends have the same SSL problems with Thunderbird as I have with Postbox. They also have the same ISP as me (dslextreme.com).

Mail settings are as follows:

pop.gmail.com
smtp.gmail.com

I will show 4 screenshots.

I have more.

Many thanks, lukor