Since yesterday, March 25 (I started to see it around 8:00am EST), ORDB.org - one of the old SPAM blocklist databases - started to blocklist (or block ;)) all IP addresses. As a result, all mail servers using an SPAM filtering solution that still references ORDB (relays.ordb.org) started to immediately block all incoming e-mails. I got some reports into my personal e-mail yesterday, that finally got fixed by my provider today.

Although ORDB.org was shut down on December 18, 2006, yesterday they changed their behaviour, and instead of timing out, they are blocking all IP addresses, that is, every e-mail server queried is being reported as an open relay. If your mail infrastructure uses ORDB, the sender will get a message like this one (this is an example blocklisting the Gmail servers):

Technical details of permanent failure:
PERM_FAILURE: SMTP Error (state 13): 550-Message rejected because ag-out-0708.google.com [72.14.246.240]:20081 is
550-blocklisted at relays.ordb.org see ordb.org was shut down on December 18,
550 2006. Please remove from your mailserver.

E-mail administrators (if you have not been notified yet by users not getting a single e-mail during the last 24 hours), please, check that your SPAM filtering solution is not querying ORDB!

(...and there are lots of them using ORDB by default)

The real reason behind this active behaviour change is not clear yet.
--
Raul Siles
www.raulsiles.com