mail delivered despite quota limits

I've been experimenting with using procmail to deliver mail to
a user's home directory where quotas are in place to control
disk usage. In my experiments so far, the mail is either delivered
with no error or is silently lost into the great bit bucket when
a user is over quota. I am doing this via a .forward and simple
procmailrc in the user's home directory. Has anyone had such
an experience and found a solution.