I've used this
spreadsheet to forward existing messages. Works like a charm.
This version is a copy of a tool I found online. I added some functionality to it. Attributions are in the code.
Main Steps:
1. In the to-be-forwarded account, make a label in Gmail and move all the messages to be forwarded into there
2. In the to-be-forwarded account, make another label in Gmail that will contain all of the forwarded messages once they've been forwarded
2.5. Highly recommended: In the destination email account make a label and a filter rule to receive the forwarded messages. Otherwise prepare your inbox for a flood.
3. In the spreadsheet, put the two label names in the right places (A1 and D1), as well as the destination email address (B1)
4. Run the code manually from the menu (useful for forwarding existing messages) and/or configure it to run automatically (useful for forwarding new/incoming messages ... especially in a GAFE domain with forwarding disabled ;-) Instructions are in the sheet.
Joel
PS: You'll need to make a copy.