Q: Delete letter after forwarded copy is *received*?

I want to keep a copy of each forwarded message.  But after I am sure the
forwarded message has been *received* I want to delete the unforwarded copy in
my home location.

I am looking for a recipe that will keep a backup copy of each forwarded
message in the home directory, then delete this backup copy after the forwarded
message has truly been received.

Any ideas are appreciated.

-Andy