550 Requested action not taken: mailbox unavailable Sender address has null MX

Reason

The email could not be delivered because the sender domain is using the "Null MX" - No Service MX Resource Record - via DNS to indicate that it will not accept any email.

We only accept emails if it is also possible to send an email to the sender domain.

Solution

The owner of the domain must publish an MX record in the DNS that allows emails to be accepted.

For more information, see the RFCs at the following links:



See also: General information on our error messages.