MailRedirect is an extension for Mozilla Thunderbird that does just that: it redirects an email. The difference with forwarding is subtle but important: the email will seem to be originally addressed to whoever you decide.
I find this useful when I get an email that I want to be preserved while transferring it to the right person.
Of course this means anyone can now get an email and pretend it was never sent to them. The content can’t be changed before redirecting an email (or bouncing it, which is the correct term in mail-jargon), and there’s been quite some discussion around the security implications.
I intend to use this as a demo of what can be accomplished with Mozilla extensions, which can be damaging in the wrong hands 🙂