On 2017-04-19 12:15:06 (+0200), David Hofstee <[email protected]>
wrote:
2017-04-19 3:50 GMT+02:00 John Levine <[email protected]>:
In article <[email protected]> you write:
However, under RFC 5321, section 5.1, I had always thought that
without an MX, the system should revert to using the A record as an
implicit MX.
You are correct.
On the other hand, these days domains that expect mail generally do
have MX records, so I can't blame them for treating the lack of MX as
a signal that the address is bogus.
It may have to do with squatted/parked domains and/or port 25 being
closed by a firewall. Parked domains generally have A records for
showing ads but often do not have MX records (or an open port 25).
Instead of getting a bounce immediately, you may have to wait for a
timeout when the sender makes a simple typo.
And then there are cases when parked domains do have port 25 open
and/or an MX record. Different discussion.
The correct way to indicate that a domain does not accept email is to
have an explicit null MX record in the DNS, e.g.:
foo MX 0 .
See RFC 7075.
Philip
--
Philip Paeps
Senior Reality Engineer
Ministry of Information
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