How do I find if I have blocked the domain from sending to my server. Meaning,
knowing the
domain name of the sender, how do I find the IPs from where the mail could be
sent from. It
seems that SPF is the only tool to provide that answer?
Unless you have previous mail from the domain, I would agree SPF is your best
bet.
In another related problem, which is linked to IPv6 and RBL. Buidling an IPv6
RBL could lead
to a huge database. Sure you can alleviate by using "wildcards", but why not
use the reverse
DNS resolution to add a TXT record associated to the IP to indicate the IP is
the one of a
mail server? So any IP that does not have this record would be blocked for
SMTP.
We've had a variety of proposals to identify mail client hosts. See
http://mipassoc.org/csv/
R's,
John
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