That's exactly what I thought. We aren't looking for Internet access at this time, just pointing out that if some large cities in the U.S. can't provide reasonably priced Internet access to businesses that includes vanity reverse DNS entries, it's just plain silly to block E-mail based on the reverse DNS entry seeming like one that might appear with a dynamic or residential connection.
But if an MX looks at the number of DUL IPs that spam it, and adds up the total number of SPAM messages from those IPs, and then compares with the qty of "legit" DUL IPs and the number of msgs they send, the latter numbers are trivially small, nearing 0.
It's always the same tradeoff: do I open up to receive a 1000 SPAM msgs just in case I might get 1 or 2 legit msgs?
And often, for a given MX needing to accept traffic from a DSL/cable IP, it's very easy to whitelist those IPs.
So blocking DULs, as AOL and others are threatening, is effective policy.
If legit, mostly SME businesses on DUL/DSL/cable want to run a mail server (and how many even can do it properly (closed relay, closed proxy), even if they wanted?), the best policy (for everybody) is that they avoid all "DUL blocking" hassles by relaying their mail servers' outbound mail through the SMTP gateway of their IP provider, just like any other DUL.
Len
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