AOL is rejecting some email from my system saying that it does not have a reverse DNS entry.
FYI, AOL's current policy is that they will reject E-mail if it contains no reverse DNS entry *and* they have other reason to block the mail. They are not currently blocking solely on the lack of a reverse DNS entry.
I'm not totally sure I understand RDNS, but basically I assume that if I have an IP that matches the EHLO domain, I'm ok.
Close.
What you need is the IP address that IMail uses to have a reverse DNS entry, and that the reverse DNS entry resolve back to the same IP. It does not matter how the domain compares to the HELO/EHLO, although if possible it is good practice for them to match.
Connecting to the outside world, my server comes from 209.202.128.38. The email server identifies itself as outbound2.bullhorn.com, which maps to the said IP. Is this enough?
No. Mailservers don't care that your HELO/EHLO resolves to the IP of your mailserver -- what they care about is that your IP address has a good reverse DNS entry. Otherwise, a spammer could just create a DNS server that takes "a.b.c.d.spammer_domain.com" and resolves it to a.b.c.d. That way, they can have spamware that takes the IP that it is running on, and says "HELO a.b.c.d.spammer_domain.com", without needing a reverse DNS entry. Since reverse DNS entries are much trickier to alter, that's what anti-spam software uses.
http://www.dnsstuff.com/tools/ptr.ch?ip=209.202.128.38 shows that Exodus doesn't have a reverse DNS entry set up for 209.202.128.38. Call 'em and yell at them (or be nice, and simply ask why they assigned you an IP that has no reverse DNS entry set up).
Also, has anyone else noticed that AOL has begun accepting email, deciding to reject it as spam and then not sending an NDR? Very annoying...
Yes, they have done that for years. They have had both a public anti-spam system (that they have information about at http://postmaster.info.aol.com ), and a private undocumented anti-spam system. The private system is a weighted system that will delete E-mail, and having no reverse DNS entry counts very heavily towards it (a rough guess would be 80% of their delete weight).
-Scott
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