Try unverified_sender_defer_code option I think the problem you experienced might be affected by two options:
a) The order in which the different actions are listed in smtpd_recipient_restrictions seems to matter. I added the "reject_unverified_recipient" option last, just before the "permit" option.
b) The "unverified_sender_defer_code" option is set to "450" by default. Therefore, if a temporary error occurs during recipient verification, the server will send a temporary error to the client, resulting in the error message. By setting this option to "250", the server will accept the recipient address, if it cannot be verified right now. Thus, the server will only send an error to the client, if the address cannot be verified because of a permanent problem.
Please tell me, if this options work for you. I am currently evaluating ZCS Network Edition and for the tests I performed, it works. However, I would like to know, if it also works in other setups before possible moving our production system to ZCS. |