Releasing Items from Mailscanner Que

The easiest is to have your mailscanner configured to quarantine Whole Message as Queue files; from Chirpy with instructions for this and more, here.

Quarantine Whole Message = yes
Quarantine Whole Messages As Queue Files = yes

then to requeue the email to be delivered, you need to go to the indicated directory within:
/var/spool/MailScanner/quarantine/<date>/<message-id>/

Then you need to:
cp -av *-H /var/spool/exim/input/ ; cp -av *-D /var/spool/exim/input/
one done you’ll have to wait for the next exim mail queue run, or run it yourself from WHM > Manage Queue > <message-id> > Deliver Now