Sauer, Damon > I can't- I like the idea.. but it has to go further than that.
Example: MOMandPOP.com hosts their website and mail systems at their local
ISP.
They send email as recipes(_at_)MOMandPOP(_dot_)com(_dot_)
Because their ISP has closed port 25, all email from MOMandPOP.com must go
to the relay server first.
You see at your end-
HELO megamail1.isp.com << reverse lookup of megamail1.isp.com shows an IP
address of 198.10.10.2
mail from: recipes(_at_)MOMandPOP(_dot_)com << reverse lookup of MOMandPOP.com
shows an
IP address of 198.10.210.53
In your example, this email would fail.
No it wouldn't. You misunderstood his proposal.
He requires the rDNS of the connecting server machines the HELO of the
connecting server, neither of which would be MOMandPOP.com. Ie:
The reverse lookup of 198.10.10.2 yields megamail1.isp.com - checking
whether that matches the HELO is the trick.
This has no relationship to the mail from or From:.
Right now you can use this heuristic with a few selected servers (eg:
MSN, yahoo and excite) because you know two things:
1) They're oft-times forged in HELOs
2) Their servers _do_ have valid rDNS.
However, this is a short-lived heuristic. Enshrining it in the RFCs
would help, but, only mid-term.
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