secure lists memberships / spoofed send from addresses
I'm a member on some 'secure' mailing lists where I get an alias that I have to send from.
For example: I have my real address, email@example.com, I'm then given a forwarder on firstname.lastname@example.org which forwards mail to email@example.com. To send TO the lists on firstname.lastname@example.org I need to send FROM email@example.com.
Basically what I'm asking is is there any way to add a 'from' address for a domain that's NOT added to my Zimbra server? Obviously if I add list.com as a domain just to be able to add firstname.lastname@example.org as an identity it will recieve emails fine but bounce outbound emails as postfix will try and locally route it.
I'm assuming virtual hosting won't do what I want either, I've tried manually putting in (out of desperation :p) "me <email@example.com>" as my 'from' name which obviously didn't work as it'll be escaped :)
Any ideas? Am I missing something blatantly obvious? I've had a decent look on bugzilla for features and on the forum with no success.