Feat: Add email forwarding

[harshsbhat]

Feature request:

Inbound email forwarding services like: https://postmarkapp.com/developer/user-guide/inbound/sample-inbound-workflow

We should have a forwarding service that forwards all the emails received to one address to a previously configured forwarding address

for eg: if [email protected] is set for forwarding to [email protected]

Ideally, unsend should send the mail converted to JSON on my webhook URL every time [email protected] receives an email