A user has just reported that twice in a row a TKLBAM backup failed. Both times it choked on files in /var/spool/postfix/.... I assume because the spooled mails had sent and/or been deferred.
TBH, I'm not really sure why it's not an issue more often (I can only assume that TKLBAM already has some mitigation for this, but it's imperfect).
Regardless, a hook script to stop/start postfix when running a backup might be the best way to go?!