excessive recursion (max 50), ruleset canonify



I have Exchange 2003 Enterprise running on a cluster. Everything has
worked fine up until about 3pm yesterday. Suddenly, all external
emails to our domain were bounced with this error:

host pageinc.org [65.83.225.175]: 554 5.0.0 rewrite:
excessive recursion (max 50), ruleset canonify

Internal email works fine, and we can send email. We just can't
receive it from outside our domain. I've tried restarting the
cluster, etc. but that hasn't had an effect. Is this due to a DNS
issue or something external to our network? Or might this be
something that's changed on the Exchange server?

Any help appreciated.

.