[Mimedefang] sending relay has no MX record?

David F. Skoll dfs at roaringpenguin.com
Mon Jan 31 12:09:39 EST 2005

On Mon, 31 Jan 2005, Adam Lanier wrote:

> Technically, a server can generate mail (legally according to RFC's)
> without having an MX record.  Only servers that RECEIVE mail need to
> have an MX record.

They don't need to have an MX record; an A record will do.

roaringpenguin.com, for example, has an A record.  If roaringpenguin.com
had no MX records, then mail for foo at roaringpenguin.com would go to the
A record.

> What needs to be in place is a valid return path for the mail that is
> generated.  So, while server 'mailout.example.com' can generate mail
> from the domain 'example.com' with only an A record, some server
> somewhere SHOULD (again, according to RFC's) have an MX record for the
> domain 'example.com'.  If there is no MX record for the domain
> 'example.com' then the 'mailout.example.com' will be used as the return
> path for the generated mail.

No; if there's no MX record for "example.com", then the A record for
"example.com" will be used, if it exists.  If no A record exists either,
then it will be impossible to mail anyone at example.com


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