> Today, I noticed 3 different and unrelated email addresses whose
> domain name does not have a MX entry; 2 in one country and 1 in
> another country.
>
> A Telnet to each showed a functioning mail server (MTX) running Exim
> 4.80.
>
> Is the MX record officially redundant if one has 1 MTA ?
They aren't redundant but they aren't necessary. The standard is that
you try the A record[*] if there is no MX record.
(This behavior is actually sometimes annoying, because it means that
there is no clean standards-compliant way of saying 'this machine exists
but you should never attempt mail delivery to it'. People often use
various bogus MX values for this purpose, like 'MX localhost.' or 'MX
.'.)
- cks
[*: these days I imagine you also try the IPv6 equivalent if you have
that.
]
