avast scans out and ingoing emails from an VM

Avast Free Antivirus / Premium Security
1

https://forum.avast.com/index.php?topic=211419.0

situation: I have a windows 10 computer that has avast as anti virus security, and I have a virtualbox virtual machine running with xubuntu.

  1. emails from that system get a signature from avast in german (the virtual machine is set to english).

  2. the thunderbird within that VM can’t retrieve certificates from google.

  3. the certificates in thunderbird are from an unknown CA named AVAST! (which is weird, I never installed avast inside the VM).

and now, google decided to lock an account, and I can only guess, that the “unusual activity” means, that thunderbird does not respond correctly.

so, how do I prevent avast from scanning in and outgoing emails from said VM?