Simply look into server-mgr-antivirus panel. If it is a recent AV installation from Knudsen then there is a (re)sent-button right next to the incriminated mail. If not, update the AV installation from Knudsens site. But i cannot guarantee if the messages are kept on update.
Found at Knudsen:
Quarantined emails will be quarantined in /var/spool/amavis-ng/quarantine and Problems emails in
/var/spool/amavis-ng/problems