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.
You don't seem to realize that some people need to receive their E-mail.
Fortunately, we rarely ever get E-mails from customers that have blocked us for some dumb reason. But, when someone sends E-mail to [EMAIL PROTECTED] and needs DNS assistance, and the response to them bounces, do you really think that we are going to take the time to re-route the E-mail through another mailserver? It's a huge waste of time and resources.
Blocking E-mail because spam has come from that IP is acceptable; blocking E-mail because the IP is running an open relay or open proxy is acceptable. Those are problems that the sender can fix. But doing "bogus blocking" (my term for blocking legitimate E-mail for reasons often not under the control of the sender) doesn't do anyone any good. As I've said, it can be VERY useful as part of an overall spam control program -- *if* you don't block the E-mail, but instead count that against them. That way, a good company can prevent their E-mail from being caught, even if there is a problem that isn't under their control.
This is very much like SPEWS -- they intentionally list legitimate mailservers. Anyone who blocks E-mail that fails the SPEWS test is intentionally blocking legitimate E-mail, which is a huge waste of resources.
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?
But, there are many other ways to block those 1,000 spams. And there may be 20-30 or 100 legitimate messages that you are blocking.
And often, for a given MX needing to accept traffic from a DSL/cable IP, it's very easy to whitelist those IPs.
That's a great solution for small mailservers, that have an admin with free time to analyze all the false positives (and can allow for a VERY high rate of spam getting caught, which is nice). But that comes at a cost to both sides (the legitimate sender has to take time to report the problem, hoping that the reporting does not get caught, and the receiver needs to fix the problem). Whitelisting is a last resort for most people.
So blocking DULs, as AOL and others are threatening, is effective policy.
Yes, if you like blocking legitimate E-mail. That may work for you, but it doesn't work for most.
-Scott
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