On Fri, Jul 24, 2015 at 10:31:10AM +0300, Michael Peter wrote:
Reject the request when Postfix is not final destination
for the sender address, and the MAIL FROM domain has 1) no
DNS MX and no DNS A record, or 2) a malformed MX record
such as a record with a zero-length MX hostname (Postfix
version 2.3 and later). The reply is specified with the
unknown_address_reject_code parameter (default: 450),
unknown_address_tempfail_action (default: defer_if_permit),
or 550 (nullmx, Postfix 3.0 and later). See the respective
parameter descriptions for details.
> I am confused that is the meaning "when postfix is not final destination
> for the sender address" ?
The restriction only applies when the domain in question is not
hosted by the receiving Postfix system as determined by its address
Sender domains in the local, virtual alias and virtual mailbox
address classes are never rejected by reject_unknown_sender_domain,
they are "known" to Postfix whether or not they are "known" to DNS.