@spacedust, I can't confirm this. if it is really PayPal, and not a scammer, rdns is set properly from PayPal. This is from my logs yesterday
Feb 2 07:38:18 server smtp: 1391344698.002655 8530 < RCPT TO
:<sales@.com>?
Feb 2 07:38:18 server spamdyke[8530]: DENIED_GRAYLISTED from
: service@paypal.com to: sales@.com origin_ip:
173.0.84.226 origin_rdns: mx1.slc.paypal.com auth: (unknown) en
cryption: (none) reason: (empty)
Feb 2 07:38:18 server smtp: 1391344698.003633 8530 > 421 You
r address has been graylisted. Try again later.?
then, as any legitimate mail server would do, it tried again and mail was delivered
Feb 2 07:44:19 server smtp: 1391345059.468122 CHKUSER accept
ed sender: from <service@paypal.com::> remote <mx0.slc.paypal.co
m:unknown:173.0.84.227> rcpt <> : sender accepted
Sender accepted. Mail was delivered.
Spamdyke rdns appears, from my logs, to work very well.