imap -> addtag then bounce (remail) -> smtp [for gmail?]

dear ladies and gents: has anyone written a (linux or perl) client
application or CLI utility that can pull all the messages from an imap
server's folder, add one x-header tag to each email (e.g., the machine
and folder name), and then remail/bounce them back or to another
server?

such an application would be particularly useful for migrating to
gmail---of course, if gmail supported imap, this would be totally
unnecessary, but for now, there seems to be no old email upload
facility. (I have seen the phython solution but it works only for
local folders, and I have seen a hotmail solution, but neither
applies.)

before I re-invent the wheel, I wonder if someone has already thrown
something like this together.

sincerely,

/iaw