On 12/1/19 2:56 PM, John C Klensin wrote:
Two things are not clear from that text: (i) while the language
describing a domain name requires that the domain be resolvable
with the target RRSet containing an address RR, there does not
seem to be a requirement that whatever is at those address(es)
support an SMTP client or server.
My take on this is that the SMTP server has an implementation bug,
likely a failure to really upgrade to RFC2821 from RFC821. (I'm tempted
to cite laziness but I must also admit that the RFCs are hard to read
and the protocols have lots of corner cases that are rarely exercised -
so I'm not surprised if implementors are impatient and cut corners.
I've done that myself.)
Keith
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