Darxus, > And I'm curious if you are asking the question you mean to. What exactly > is the way postfix checks this? Specifically, I'm wondering if you're > referring to reject_unknown_client, which I've used for years, and which > does not use MX addresses. > > I don't know of an option to reject an email because the sending domain > has no MX record. As has been said, the standards require then delivering > email to the A record for the domain. I don't know how common this is > among legit mail servers, but I've certainly seen it.
reject_unknown_sender_domain Reject the request when Postfix is not final destination for the sender address, and the MAIL FROM address has no DNS A or MX record, or when it has a malformed MX record such as a record with a zero-length MX hostname (Postfix version 2.3 and later). The unknown_address_reject_code parameter specifies the numerical response code for rejected requests (default: 450). The response is always 450 in case of a temporary DNS error. The unknown_address_tempfail_action parameter specifies the action after a temporary DNS error (default: defer_if_permit). Mark
