Are you referring to the process that some MTAs follow? For example, if
a MTA needs to deliver a message, it is suppose to find a MX for the
right hand side of the email address and deliver it to the eventual A
record (Hector's claim that some MX records return IPs confused me).
Right. It is true that some misconfigured MX records contain a name that
looks like an IP address and is probably intended to be the IP address of
the server, but I'm not interested in going down the road of second
guessing all the ways that people can screw up their DNS, so we'll ignore
that.
Some MTAs, when they don't find an MX record, just lookup an A record
instead and deliver to the resulting IP.
That should be ALL MTAs, since the RFCs have always said that's what you
do.
If that's the case, shouldn't the deprecating of A lookups when a MX
lookup fails be brought to the SMTP group?
I'm sure this has come up before, but it's probably worth running by them
again. This was intended to be a transitional feature 25 years ago, and
given how few legit MTAs are identified by A records, we should try to
declare the transition to be over.
R's,
John
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