Outlook 2013 Searching Issue

I have a client that is having a serious issue with searching.  When they search for a particular email such as (ex. Robert Love) all emails does not show.  If the email came in or went out as (ex. rlove@) when searching Robert Love it doesn't find it which it should.  I have went into options - searches and uncheck the box for instant searching.  I also went into the account and made sure cache mode was checked and the bar was move over for all emails not just 12 months.  What am i missing?