I want to achieve the following with postfix:

Almost all outgoing emails shall be sent via a relayhost, configured in main.cf with

relayhost = my.mailserver

There's one specific email address ([email protected]) for which I want the email to be delivered locally. I set up a local account on the machine to match the email address and added "mydomain.com" to the mydestination property in main.cf. Then of course postfix tries to deliver every email to @mydomain.com locally and bounces them because the respective user doesn't exist.

Question http://serverfault.com/questions/149453/hybrid-gmail-mx-postfix-for-local-accounts seems to be somewhat related (though more complicated).