[Exim] Stopping Quota Bounces

I seem to recall this subject was touched on as part of another thread a
few weeks ago, but I couldn't pull any real conclusions from the
discussion.

The recent thread about frozen messages brought the thought back up in
my head. The vast majority of the frozen messages in my queue are
attempted bounces to spam sent to users who are at their hard disk
quota.

I prefer to use disk quotas to any other system because the users get
both web space and e-mail storage in their home directory. They can
split that up any way they want. I specifically have the /home file
system formatted with XFS because of its excellent quota support.

Anyway, to the question... How can I stop the bounces generated after
the fact by users at quota? I worked to have nearly all my rejections
done at SMTP time, but this quota thing has been a thorn in my side.

--
Chris