For instance, they are bigisp.com (this is the domain used by their
retail/residential customers), but I get spam from
x-x-x.pa.client.bigisp.com and x-x-x.nj.client.bigisp.com where the
former is covered by an SPF record and the latter is not. It would
seem that a wildcard at *.bigisp.com would help them out.
This is more of an argument for something like MTA Mark, since those
client addresses are cable modems that shouldn't be sending any direct
mail at all.
A few other people wrote and pointed out that cjb.net is a free mail
redirection service that has for a long time useds *.cjb.net to catch all
the mail and then route it internally.
Someone else pointed out that there's an MX for *.cnn.com and
*.turner.com, presumably so that CNN can route subdomains internally.
Anyway, it remains clear that there's a lot of wildcard MXes in use, and
we can't gratuitously break them.
Regards,
John Levine, johnl(_at_)iecc(_dot_)com, Primary Perpetrator of "The Internet
for Dummies",
Information Superhighwayman wanna-be, http://iecc.com/johnl, Mayor
"I dropped the toothpaste", said Tom, crestfallenly.