Wrong.
It’s clearly an advertisement that says specifically:
“This email has been sent from a virus-free computer protected by Avast.” with a linked logo and URL to Avast’s site.
The logo itself is a track-able image served by avast:
https://ipmcdn.avast.com=/images/logo-avast-v1.png

There’s posts from 2014 that suggest they’ve been doing this for the free version all along.
Being a PAYING CUSTOMER, I’m extremely angry that this was ‘accidentally’ enabled on the latest paid update.