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

[Jonathan de Boyne Pollard]

KD> some misguided mail servers/admins use reverse lookups as a 
KD> kind of litmus test for spam (as if spammers couldn't come 
KD> up with their own reverse records, duh).

... which, of course, they do.  And as a consequence these misguided
administrators come up with ever more convoluted, arbitrary, and fallacious
DNS-based tests to apply, and cause more and more false positives as a
consequence.  Today's example of such tomfoolery is Outblaze.  It has been
reported today that it is now applying a test such that the SMTP Relay client
IP address must map via DNS lookup to a "real domain name", where Outblaze has
a rather narrow and peverse definition of what "real" is that excludes many
domain names that are quite real; that that "real domain name" must have an
"MX" resource record set; and that the "MX" resource records must refer to "A"
resource record sets that in turn contain the original IP address.