[Exim] Re-spooling after a pipe

Hi.

I've got a pipe transport set up to pass all emails for a particular
address into a program. When the program receives the message it connects
to a database and finds out what to do with the message. If the program
can't connect to the database then it can't send the message, and so the
message gets lost.

I'm looking for a way to re-spool the message after it's been delivered
(via the pipe) to a program, so that exim can pass it back into the
program the next time exim runs through it's queue.

Is this kind of thing possible, or should I handle it all myself from
within my program?

Thanks.

--
Graham Ashton