It might be a little helpful, if you
1) told us which email program you use
2) clued us in as to which version of Windows or Mac OS you are using
3) listed any error messages that appear when you try forwarding (if there are any)
4) tell us if you've tried using the keyboard shortcut to forward an email
5) tried reinstalling your email software
6) done a Google to see if you can find the answer that way