Yes AVG is known to interfere and block alot of mail clients including eM CIient when the mail shield is enabled. Most users normally disable the shield so AVG “is still running resident and still working”, but just not interfering with the mail coming in or out.
You can try the following though in AVG.“which has worked for some users”. If the below still doesn’t fix the problem, then you will have to contact AVG technical support for assistance.
Allow eM CIient into AVG (Blocked and Allowed apps) section. See AVG website . Scroll down on the page for the heading “Add and Allowed app”. Or go to their support home page and type “Blocked and Allowed apps”
Also (export the AVG certificate) and then (import the AVG certificate) into eM CIient. See AVG website how to export the Mail Shield certificate. Or go to their support home page and search for “Export Certificate”
(Import AVG Mailshield Certificate into eM Client V9 & 10 Beta)