Replicate Fastmail's "Send Via" Functionality

[Chris Godbout]

Quite a few years ago, I used to use Fastmail, but have hosted my own mail for a while. One ability I miss was the ability to add different identities and assign them different SMTP servers. This way, I could log in with one account and my from address would determine how the mail gets sent.

Here's my setup: my school's email (m...@school.edu) and my personal mail (m...@mydomain.com) both get forwarded to m...@mydomain.com. I own and control mydomain.com, but have no control over school.edu. At the moment, I've just been adding a dummy account on my email clients that can basically only send mail.

I'd like to be able to login to my server as m...@mydomain.com and send as either m...@school.edu or m...@mydomain.com and then have postfix determine whether to relay the email directly (when it's sent as m...@mydomain.com) or to use my school's mail server (when it's sent as m...@school.edu).

Does this make any sense at all? Is this even possible with postfix?