Reverse Dns Question...is it really necessary or not?

[Barry Margolin]

In article <cdjig9$1p1r$1 at sf1.isc.org>, Chip Mefford <cpm at well.com> 
wrote:

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> Simon Hobson wrote:
> | Chip Mefford wrote:
> |
> |
> |>They may indeed have address->name mappings, but very seldom does
> |>one have an MX record. Not MX record, then it is not a legitimate
> |>mail relay.
> |
> |
> | Can I clarify what you mean here ?
> 
> Sure.
> 
> | I read it as, if the mx record doesn't match the sending IP address,
> | then the sending machine is not legitimate. That makes all our
> | outgoing mail illegitimate then !
> 
> No, however a lot of folks (and I have *NOT* done this) use the MX
> mapping thing as a rule in their spam fighting attempts.
> This would be folks like compuserve in europe, apple.com aol.com and
> some others.

I find this difficult to believe, since I think they would end up 
rejecting mail from themselves!  I'm virtually certain that AOL uses 
different servers for incoming and outgoing mail, so their MX records 
won't have any relationship with the servers that send out their mail.  
This is considered best practice for large ISPs, so it's totally 
impractical for other large ISPs to perform such checks.

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
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