Problem:

You're getting the following error message/bounce when you send an email which references relays.ordb.org or ordb.org blocklists:

554 5.7.1 Service unavailable; Client host [xx.xx.xx.xx] blocked using relays.ordb.org

Resolution:

NOTE: this ONLY APPLIES if the bounce message specifically references these blacklist/blocklists:  blocked using relays.ordb.org; ordb.org

The problem is that the recipient's ISP is using this blocklist service which is NO LONGER ACTIVE AND as of 3/26/08 was updated to "list the entire world"... i.e., ANY AND ALL IP ADDRESSES ON THE INTERNET will show as listed on this blacklist.

Details about this issue with relays.ordb.org/ordb.org can be found at this URL: http://www.dnsbl.com/2007/02/status-of-relaysordborg-dead.html

Specifically, they have posted this CRITICAL UPDATE which clarifies the issue and identifies that ANY MAIL SERVER USING THIS BLOCKLIST WILL REJECT 100% OF ALL MAIL:

3/26/08 Update: ORDB has "listed the entire world" -- returning any query with a "listed" response. The result is that if you still have ORDB in your mail server config files, you're now blocking 100% of your inbound mail. For anyone still trying to "use" ORDB, you're not going to receive any inbound mail until you disable queries to it.

To resolve, you need to contact the recipient - they need to contact their ISP, and inform them to IMMEDIATELY stop using relays.ordb.org or ordb.org as a blocklist service for mail filtering.