Custom 550 5.1.1 message

[Mark Edwards]

I would like to issue a custom message for 550 5.1.1 errors, on a per- 
user basis.  In other words, instead of the generic

Recipient address rejected: User unknown in virtual mailbox table


that goes out now, I want the ability to override that with a message  
saying something like:

	<username> is no longer valid; please contact <person> at <new-email- 
address>.

Is such a thing possible with Postfix?  Thanks!