So ordb.org has been dead for awhile. If you had an inactive server that was using ordb.org as your Realtime Black-List server on that box and you bring it back up then you won’t accept email from anyone any more. Reason being is that every time your server goes to receive an email and does a lookup on an RBL if it cannot reach the RBL then it will receive no email. Furthermore if your server cannot communicate with the RBL server then you will reject mail. So while RBLs will save you from massive amounts of spam they can actually be used to attack your server. For example, the DNS server you use as a lookup – if someone were to put a man-in-the-middle or poison your capacity to communicate with that server – and you were using the DNS name of an RBL then you would essentially stop receiving mail. It’s a back-handed way of performing a Denial of Service attack, but still a way to do so. So your ability to receive mail becomes contingent upon the security of all up-stream RBLs since each message gets checked against each RBL database…
