They'll keep on coming back, that's your Gmail message cache directory that Thunderbird keeps a local copy in.

Most of them are fairly low risk email borne hazards that are likely being detected months or years after delivery.

You can always look at the quarantine folder to see what the messages are, and then delete them from your Gmail account of there is and unnecessary.

Graeme

From: clamav-users <clamav-users-bounces@lists.clamav.net> on behalf of Bud Rozwood via clamav-users <clamav-users@lists.clamav.net>
Sent: 19 May 2020 02:19
To: clamav-users@lists.clamav.net <clamav-users@lists.clamav.net>
Cc: Bud Rozwood <budroz89@gmail.com>
Subject: [clamav-users] Possible threat in thunderbird?

Hi,

I ran clamscan on my ~/.thunderbird directory and clamscan detected
these files (log attached) as threats. I didn't know what to do with
them or if I should worry so I decided to post them as described in the
FAQ. I've at least quarantined them to a separate directory, which I'm
not sure if it was wise or not but thunderbird still appears to be working.

Advice?

--
Bud Rozwood