I'm not fully convinced that they're the best tags, but forwarding and email-forwarding seem to be covering the exact same territory.
forwarding has usage guidance:
Generically refers to the operation of re-sending an email message delivered to one email address on to a possibly different email address.
email-forwarding does not.
However, email-forwarding is a more specific tag name and should be the master, I think. That means:
The usage guidance for forwarding should be copied/moved to email-forwarding
- forwarding should be made a synonym of email-forwarding
- forward, currently a synonym of forwarding should be changed to be a synonym of email-forwarding
- forwarding and email-forwarding should be merged