unverified recipient tempfail response

[Morten Stevens]

Hi,

Is it possible to define a custom tempfail response for unverified 
recipients?

For example:

unverified_recipient_reject_reason = User unknown
unverified_recipient_reject_code = 550

rcpt to: <t...@example.org>
550 5.1.1 <t...@example.org>: Recipient address rejected: undeliverable 
address: User unknown

That's right so far.

But if the backend server is not available, postfix also responds with 
"User unknown".

450 4.1.1 <te...@example.org>: Recipient address rejected: unverified 
address: User unknown

I would expect something like this:

450 4.1.1 <te...@example.org>: Recipient address rejected: tempfail: 
please try again later

Is that possible? Something like 
unverified_recipient_tempfail_reject_reason = tempfail: please try again 
later

Thank you.

Best regards,

Morten