That is all well and good, but it is completely of value to the receiving
MTA, and under their complete control. There is nothing that requires a
receiving MTA to follow this model, despite what others may see as value.
well, if you want to receive mail from other domains without special
arrangement, you need to specify in DNS how those other domains should
send mail to you. and you do that by following the instructions in the
mail standards, rfc2821[bis] in particular.
if you don't want to receive mail from other domains, or if you're
willing to make special arrangements with the domains from which you
wish to receive mail, you have no particular requirement to follow the
specifications for how to advertise this in DNS.
but hey, if you're willing to work out your own way of doing something,
you don't need standards. that's not what standards are for.
I agree that if an MX exists, the operator of the receiving MTA has stated
its expectations, and the sending MTA needs to oblige. That is not the same
as mandating that every organization has to follow the same model.
again, they only need to follow that model if they want to receive mail
without making special arrangements with the sender. if they want to do
arbitrary things, like use a different mail transfer protocol or a
different port or a different way of advertising things in DNS than the
standards say, they're welcome to do so - but they shouldn't expect to
If there were some serious technical consequence for lack of the MX record I
all for specifying its use. Operational practice with A records shows that
there is no real issue,
only if you ignore the problems that have been observed and the
increased likelihood of such problems occurring in IPv6.
IETF mailing list