@Asyn
OK now for OUTGOING emails but not for INCOMING emails.
If I send an email to my Outlook.com account now, it has the Avast marker at the bottom - OK for send from Thunderbird.
If I REPLY to this back to Thunderbird, the Avast marker is at the bottom, after the sent copy.
If I send a new email from Outlook.com to Thunderbird, the incoming email in the Thunderbird Inbox has NO Avast marker !
It is the INCOMING emails I need Avast to check NOT the OUTGOING.