I would like to use Zimbra's postfix as an unauthenticated outgoing SMTP relay for mail originating from localhost and all RFC1918 addresses in the Zimbra server's subnet. I happen to like the mutt MUA so I'm using it on localhost as the testing client. This applies only to mail sent from a MUA besides Zimbra's web interface, which is lovely...but it's all about choice, right? Anyhoo, Here's where I'm stuck.

Open mutt with
Code:
mutt -f imaps://localhost/INBOX
then login as normal. View messages in inbox. Create new message to address external from Zimbra domain. Set From: user@zimbra.domain header in mutt. Send message. mutt reports message is sent successfully. Message never reaches it's destination. There is no bounce. It's gone. Running
Code:
/opt/zimbra/postfix/sbin/mailq
says queue is empty, so the message must have gone somewhere. But where?