How to change the respond with error code 450 to 550


New Member
Jun 21, 2023
I enable the Reject Unknown Clients to YES.

postfix/smtpd[12695]: NOQUEUE: reject: RCPT from unknown[172.xx.xx.xx]: 450 4.7.25 Client host rejected: cannot find your hostname,

I already Verify receivers to YES (550) but issue is the same.

my goal is to block all incoming domain and whitelist the trusted domain

Thank you.
These mails are rejected because they don't have a matching forward and reverse DNS entry (or because your PMG's DNS setup is broken)
In general a temporary error makes sense in this case (as the admin of the remote system could fix their configuration in the meantime)

But you can adapt the postfix configuration to send a permanent error in those cases.

The settings are `reject_unknown_client_hostname` and `reject_unknown_sender_domain` - and the postfix documentation on those settings:
points to
see 4.7.4 in

To adapt the postfix configuration in PMG you need to use the templateing system:

I hope this helps!
Thank you for response.

But if the Reject Unknown Clients is disable. All email is fine can send and receive with no block.

Our email server is MS exchange.

Thank you.


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