[exim] Send a maildir to exim to be sent

I wrote a system_filter to dump bounce messages into a maildir, but
unfortunately it turned out to be over enthusiastic and has dumped
_all_ messages going through exim.

I now need to resend about 50,000 messages that are in a maildir. Is
there any easy way to do this?

Many thanks for any pointers, or even just hints on good things to
google for related to this.

Ed