[Exim] delayed 24 hours warning message

one of my users has a full mailbox, so his incoming mails are all sitting in

the queue.
one mail has now been in there 24 hours, so exim sent a warning message to
the sender,
but reason in the warning message states:
     Delay reason: Retry time not yet reached
how would i get the reason to state the actual problem, that his mailbox is
full?