Cause: 

A normal CA search uses the Department ID tag applied to the message during the archiving operation.  This Department ID tag provides for a more efficient search.  This search behavior can be changed to use the emails addresses of certain or all of the Department's Monitored Employees by clearing the check box by the Department name and populating the check boxes next to the Monitored Employees that are to be searched. This type of search is called a 'Legacy Search'.  When a legacy search is used, the Department ID tag is not considered.  This allows items for Monitored Employees that were were not Monitored Employees during part or all of the search date span to be returned.

When using a legacy search, the pattern matching used with the email addresses can provide hits for users that have data preceeding the criteria.  For example, with searching for 'smith@mydomain.com', mails for 'john.smith@mydomain.com' will also be returned because the pattern match finds the 'smith@mydomain.com' portion of the address.

Solution: