@leona65,
In short, EITHER Avast takes care of SSL by configuring Avast settings for it, or it is your email client (the program you use to read, send and retrieve your emails) that is configured for SSL. Not both.
So, as already explained, if you configured Avast correctly to take care of SSL, it's perfectly fine (and desired) to deselect (unselect, uncheck, unset) this option in your email program.