I notice from your email icon, you have a gmail account, is this the email you are downloading or do you have other accounts ?

avast, can’t scan SSL/TLS secure encrypted email, that is the whole idea of secure email to stop people (including AVs) poking there noses in your email. Gmail scans its emails so you have at least some protection there even if avast can’t. However if you want avast to scan it you need a third party interface such as STunnel that allows avast to scan content before it is encrypted, etc.

Other topics:
Gmail and Avast Providers
Redirecting multiple SSL accounts