This is a problem that appears when trying to send to internal accounts, ie the accouns from the same server.
When we send to a non existent account, it is normal to have a bounce. But when the account is internal, the message cannot be sent, getting an error:
Message not sent; one or more addresses were not accepted.
Rejected addresses: firstname.lastname@example.org
Well, this is not absolutely wrong, but it is a little inconvenient, especially when dealing with hidden GAL. There are times when a message has to be sent to some douzens or even hundreds of recipients, and if a number of those are either closed, in maintenance or non existent, then the message cannot be sent AT ALL. One has to go through the entire list of accounts in the message header to delete or alter the problematic one, only to have to redo the same thing over and over, depending on the number of bogus, actually, addresses.
It's not a postconf issue, internal delivery does not include mta's. We would love if there was some configuration option to just ignore inexistent accounts rather than abort sending to them. Or, as in extend, to simulate MTA behavior, accepting the message and bouncing if errors or warnings occur.
Once more, I repeat that this is about INTERNAL accounts.
I haven't been able to find any such post elsewhere.