From: Hadmut Danisch <hadmut(_at_)danisch(_dot_)de>
1. an SMTP server first compares the reverse DNS name of the SMTP
client with the sender domain. If they match by the usual rules
(e.g. user(_at_)example(_dot_)com matches mailhost.example.com), then
the STMP
client is authorized. To prevent forgery, the usual reverse-forward
DNS check is made.
This doesn't work in common. A host can have only one reverse DNS
name, but deliver for many different domains.
That check is only the first check. If it fails, then no harm is done.
Moreover, as was recently discussed in this mailing list, a host can
have many reverse DNS names. See the thread that contains
https://www1.ietf.org/mail-archive/working-groups/asrg/current/msg04280.html
Note that I've removed the test case mentioned in that message.
If there is any doubt that it worked, I can easily restore it.
Vernon Schryver vjs(_at_)rhyolite(_dot_)com
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