Is there an RFC declaring what type of connection sending hosts should communicate via SMTP? I'm sure there is open proxy/zombie using a SDSL or T1 line somewhere on the internet.
I admit that I agree with you about the Reverse DNS. I assumed that since there was an entry that was enough. I am a little surprised that this issue hasn't come up before.
adamc
William Van Hefner wrote:
Jason,
I can't speak for anyone else here, but my opinion of ADSL Ips sending e-mail directly to my servers is that it should be shot on sight. At best, maybe .1% of mail coming directly from ADSL connections is legitimate, and I'm being extremely gracious with that number.
Yes, it is possible to have a "legitimate" mail server set up on an ADSL line with a subscriber network RDNS. It is also theoretically possible to host a "legitimate" mail server on a dial-up connection, on an open proxy, on a server with an open relay or on an IP range in China that has been blacklisted by every single DNSRBL in the universe. There are all kinds of remote possibilities. I draw the line when 99.9%+ of the traffic is spam. At least with Imgate the odd legitimate sender receives notice of the delivery failure, unlike with Scott's weighting system.
Anyone who goes the cheap route and routes all of their e-mail via a single MX on an ADSL connection without bothering to configure RDNS is truly getting what they pay for. If a company can't justify the money to spend on at least getting a dedicated SDSL circuit or fractional T1, then they really need to rethink their IT strategy.
William Van Hefner Network Administrator Vantek Communications, Inc.
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