Given that something like 8.13% of of the hosts that have sent non-spam mail to me do not have reverse DNS information recorded, the fact that AOL have just switched this on as a requirement will be interesting:
: jm ftp 1019...; dig aol.com mx aol.com. 3559 IN MX 15 mailin-01.mx.aol.com. mailin-01.mx.aol.com. 92 IN A 18.104.22.168 ... : jm ftp 1020...; telnet 22.214.171.124 25 Trying 126.96.36.199... Connected to 188.8.131.52. Escape character is '^]'. 220-rly-za01.mx.aol.com ESMTP mail_relay_in-za1.6; Thu, 22 May 2003 15:09:54 -0400 220-America Online (AOL) and its affiliated companies do not 220- authorize the use of its proprietary computers and computer 220- networks to accept, transmit, or distribute unsolicited bulk 220- e-mail sent from the internet. Effective immediately: AOL 220- may no longer accept connections from IP addresses which 220 have no reverse-DNS (PTR record) assigned. ^] telnet> q Connection closed.