Today I went through a very interesting experience, courtesy of AOL. I have a mail server sitting on a Time Warner Business Class line with a static IP address. TWC has assigned a reverse DNS entry for it based upon their scheme of choice. Now, AOL is rejecting emails sent from this server, because they appear to be sent from an IP address typically used as a dynamic IP, with a reverse DNS entry that does not meet certain criteria.
Apparently, AOL is using this type of filtering in an attempt to reduce spam. While I appreciate the fact they are trying to cut down on spam, I think that this approach, particularly as they have implemented it, is ridiculous.
First of all, having an IP address in rr.com's block that gets handed to cable customers does not mean that it is a dynamic address. Second of all, TWC's Business Class customers are on an IP block separate from the consumer grade cable modems. Third of all, how a particular ISP chooses to assign hostnames to their reverse DNS entries has positively nothing to do with whether or not spam can be sent from that address.
What makes this even more astounding is that without my own mail server, my choices would be to be limited to 10 MB emails, or pay more to TWC. On top of that, TWC and AOL have the same parent company! If TWC is trying to get lower level customers to choose their service over T1s or fractional T1s, then it is in their best interest to make sure that their customers can send and receive email from servers that they have, and not necessarily use TWC's. For AOL to then turn around and say, "no, we reject that email because the SMTP server is on a cable modem
Justin James is the Lead Architect for Conigent.