I have a script that has been working out SPF records for domains, and
I've noticed that some of them are more complex than desirable owing to
the lack of forward mappings from name to ip. In particular, this often
happens for the names that are the result of a reverse lookup.
Consider a user who is on a DHCP cable modem network. They want to be
able to send mail directly out. However, owing to the DHCP nature of
their connection, they can only restrict their sending addresses to the
ISP. But the ISP just assigns names to those DHCP addresses that do not
have forward mappings. For example:
For example: 200.232.161.241 maps to 200-232-161-241.dsl.telesp.net.br.
but this latter name is NXDOMAIN
This makes it difficult for the end user to select a suitable SPF
record. Maybe those ISPs need educating.....
Just an observation
Philip
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