RE: Reverse DNS - where is it?

[Scott Klement <midrange-l@xxxxxxxxxxxxxxxx>]

> I've never seen a mail server with that requirement. After all, what
> happens if you send mail on behalf of many different companies? Hell,
> not even AOL is that crazy.

You're wrong.  Verifying that the forward and reverse DNS match is very
common -- the reason is that the DNS for the IP address is controlled by a
large ISP that owns the address.  That makes it very difficult for
spammers to work around the problem -- they can't just set up a DNS
server, because the IP address won't point to it.

However, what I think you're confused about is that the forward/reverse
isn't for the domain name in the e-mail address -- it's for the name of
the mail relay itself.

When your SMTP server attempts to relay mail to someone's mail server that
implements this check, that mail server will take the name you send in
your HELO greeting and look it up.  If it matches the IP address that's
connecting to it, then it does a reverse lookup.  If that also matches the
domain name, it accepts the mail.

I know that my e-mail server's forward and reverse lookups do not match.
I therefore have to relay through a smart host with my ISP, or a lot of
the e-mail gets discarded.

> However, it's possible that some service that Centennial uses has that
> IP block flagged as a dial-up block. I've seen lots of mail servers that
> won't accept from a dial-up block.

That's also possible.