It appears that the actual text of the email, which included several urls to gif images about some time management seminar, was hosed up somehow and incomplete.
Apparently, exchange would try to deliver it, choke on the incomplete message, lose its mind, and then try to send it again, choke on the incomplete message, lose its mind, and then try to send it again, choke on the incomplete message, lose its mind, and then try to send it again, choke on the incomplete message, lose its mind, and then try to send it again...
We were able to get at the queued up messages via the exchange web interface, instead of outlook, and delete all the offending junk.