I have had the same problem since 9/9/2022. Rather than completely turn off Avast I found that I could receive emails again when I unticked "Scan inbound emails (pop3,IMAP 4)" in Mail Shield. Go to Settings, Protection, Core Shields, Configure Shield Settings, Mail Shield.
Subsequently found that my outgoing emails were also being blocked. Solved this by also unticking "Scan outbound emails (SMTP)".