OL98 Missing .dll’s

My OL98 got corrupted, evidently from bad e-mail. Now I cannot get the messaging feature to run properly and have unistalled it and reinstalled it several times. We use MS Mail and I cannot get that service to appear in order to install it. Plus when I try to view properties for Internet e-mail, I get a message that .dll’s for the service are missing.

How should I proceed?