There are a couple of items I think should be distinguished that may affect everyone's point of view.
<snip some very good comments>
So...I think that's what this whole discussion comes down to...cost and benefit. Multiple test rejection is great, but as volumes grow you just can't rely on it solely unless your willing to accept the exponentially increasing costs. At some point, you've got to start adding some single failures in.
Good points, all of them. Many single tests are sufficient for most people to reject on regardless of the results of other tests. A few I can think of:
-RCPT TO: a non-existent user. Self explanatory.
-MAIL FROM: a sender that isn't a syntactically correct email address or from an invalid domain. If I can't reach them by email, why should I accept theirs?
-HELO as my MTA's IP address/hostname and it isn't my MTA. My MTA can't send to itself from outside itself.
There are probably more I'm missing and some I've omitted since I'm tired of typing already today. If I reject on these alone, I'm saving resources (processor, disk, bandwidth, etc.). Why waste those resources on other tests when I know these should be an absolute reject?
There are also some tests I may not want to rely on alone but in conjunction with other tests, they allow me to make an accept/reject decision.
Again, IMHO the best combination is a carefully balanced mix between single failure rejection AND weighting.
Very good advice. The issue, just like spam, isn't black and white.
-- Chris Scott Host Orlando, Inc. http://www.hostorlando.com/
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