Clearing Notifications Log

Whenever I turn sendmail on, Nagios emails me about 2500 emails with the previous states of services and hosts. How can I clean out the previous entries and start fresh. I only want to get emails from the current date. I am not sure how to clean out the previous messages, or the file that contains them. Any suggestions much appreciated.

I suppose those are messages that were held in snedmail queue. If you would like to disable that, you should disable notifications from Nagios when turning off the sendmail, or empty the sendmail queue before starting it.