Not real happy have to disable email scanning
You have to normally import the Avast certificate into eM Client and also Allow eM Client into Avast as an allowed app.
See the below Avast documentation on how to export and import the Avast certificate into eM Client and also allow eM Client into Avast.
How to troubleshoot email client warnings about invalid server certificates | Avast 3
Using the Blocked & Allowed apps settings screen in Avast Antivirus | Avast
Also see this “AVG example below” in the following thread for exporting and importing the Avast Certificate into eM Client, and allowing eM Client into Avast. They both have very similar almost identical GUI’s when I tested them recently.
https://forum.emclient.com/t/almost-total-failure-after-update-to-v9/81414/41