Dears, When I checked the description of "reject_unknown_recipient_domain" on official portal: http://www.postfix.org/postconf.5.html, I found the description is ambiguous with the implementation.
Below is the quote from portal: *reject_unknown_recipient_domain*Reject the request when Postfix is not final destination for the recipient domain, and the RCPT TO domain has 1) *no DNS A or MX record* or 2) ....... >From the description, If one domain has no DNS A record or no DNS MX record, it will be reject as unknown recipient domain, however, the implementation is: It will check MX record first: a) if exist, treat as known domain directly; b) if not exist, check if A record exists; So truth is that only reject if *no MX record and no A record*. Just my 2 cents. Regards, King