Exchange Server 5.5

I need to turn off the LOGON event monitor on the exchange server. In exchange I have all the Diagnostic Logging set at none, but my event log on the server is full of logon events. This seems to happen when a user has granted a person a deligate tohis or her mailbox. I get an event stating that Mary has loged onto Joes mailbox. This makes it very difficult to monitor the server log.