Below is a list of steps to troubleshoot issues with email forwarding not working in Exchange:

1. Check the recipient mailbox to ensure that the user has forwarding rules configured.
2. Make sure the recipient mailbox is enabled in Exchange.
3. Verify that mail forwarding is correctly configured on the recipient mailbox.
4. Check the Exchange server logs to detect any errors relating to mail forwarding.
5. Check the Exchange server mail flow policy to ensure that external forwarding is permitted.