SMTP server response on client reject

reject_code

This parameter specifies the SMTP server response code when a client violates the smtpd_client_restrictions rule that is:
Access denied: SMTP client hostname rejected

Note that the postfix default value used for reject_code is code 554, and this code in 'standard RFC 822' should means 'Requested mail action rejected: access denied'. So with Postfix, a smtpd_client_restrictions rule violation does not reflect exactly the RFC822 explanation of reported code.

To avoid confusion, you can change this to 575 for example (another reason is that code 554 is also the postfix default value for other kind of errors), otherwise, do not change this unless you have a complete understanding of RFC 822.