> On Nov 13, 2018, at 11:48 AM, Wietse Venema <wie...@porcupine.org> wrote:
>
>> It's colonel.com.pl. Please check. I don't see anywhere MX's IP as A record
>> in dns zone.
>
> You have both A and MX records for colonel.com.pl. Some SMTP systems
> may try to send email using the A record, if those SMTP systems are
> borked and if their DNS resolver is borked.
In other words, nothing to worry about. There's no need to worry about
such broken systems in practice. Real MTAs don't get this wrong (though
perhaps what I'm saying is that if there are some MTAs that get this wrong,
they are garbage that deserves to be ignored).
--
Viktor.
[1] https://en.wikipedia.org/wiki/Infinite_monkey_theorem
