John,
Permissions need to be changed in the admin panel to lock out "guest" from being able to post, send emails, or PM's. This is a simple, 5 minute change you can do in the background this AM.
Spam-O-Matic uses an algorithm and an assortment of IP addresses in how it blocks spammers. There is a "user exemption" in the admin panel for allowing a known end user to become active in the system again without compromising the integrity of the spam program. Sure it is a pain in the rear to initially set up, but once it is, it runs in the background silently.
What you are now fighting is not an individual, but a spam bot that has latched on to this forum as one with vulnerabilities. It will continue to attack on a great level of occurrence now that the site has been flagged as such.
Bill S.