When a recipient server does a reverse lookup, will it look at all entries, or does it only take the first one?
The real question here is why do you have multiple reverse DNS entries?
The answer to your question, though, is that most anti-spam programs (and most *any* programs that look at reverse DNS entries) will only look at the first reverse DNS entry.
My understanding is that it looks at the connecting IP, does a reverse lookup on that IP, and if it matches the domain in the HELO, then it passes, is that correct?
No. Very, very few anti-spam programs care what the reverse DNS entry is. They just care that it exists, and has an A record pointing back to the same IP.
Otherwise, it wouldn't be possible for a mailserver to send different HELO/EHLO depending on what domain is sending the E-mail. Unless, of course, you use multiple reverse DNS entries, but that is frowned upon.
-Scott
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