We relay only for our own address blocks. Anything else is considered on a
case-by-case basis. This decision was made very early in my learning days,
after I'd spent half a day trying to clean out the 200,000 queued messages
that some spammer had crashed my server with.
As for reverse DNS, the only thing I have seen where it is even remotely
useful is for companies who use a reverse lookup in conjunction with a whois
trace to determine whether or not you are eligible to download a strong
encryption product. And even then, all one needs is a shell account in the
U.S. to get around that.
Lastly, where delegation of assigned numbers is concerned, any decent
upstream provider will allow you to use shadowing or aliasing to control
what's returned by reverse queries. This can even be done on a 4-host
David V. Brenner - firstname.lastname@example.org
International Services Network Corporation
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