formail -D like option to limit mailbox size

I subscribe to a freebsd mailing list which gets about a hundred messages
a day (I have gotten 6 in the last 10 minutes). I was wondering is there
a way using formail (or some other program) to keep say the last n messages?
What would happen is that I get a new message and I already have n messages,
then it will add the current message while removing the first one.

Thanks for any input.

Mark Bynum
bynum(_at_)cs(_dot_)fsu(_dot_)edu