My educated guess would be it is checked at the end of the supplied
options for smtpd_recipient_restrictions, is that correct?
On a very short glance at the source code, your guess does seem to be
correct.
src/smtpd/smtpd_check.c:
/*
* If the "reject_unlisted_recipient" restriction still needs to be
* applied, validate the recipient here.
*/
if (var_smtpd_rej_unl_rcpt
&& status != SMTPD_CHECK_REJECT
&& state->recipient_rcptmap_checked == 0
&& state->discard == 0)
status = check_recipient_rcpt_maps(state, recipient);
However, I am not very familiar with the Postfix source code.
Maybe somebody closer to the code can give you a more absolute confirmation.
Cheers,
K.
