Some emails not visible in OLK inbox, but are in OWA

• OS Windows 7
• Office Ver 2013
• Email Server Exchange 2010 (SBS2011)

A user is unable to see emails in the inbox from select senders in Outlook 2013, and in some case with select subjects, but can see all emails in OWA.

• We used message tracking to confirm that emails were arriving from senders at the Exchange Server.
• We next ensured Views, Filters and rules were all set to default values (in the case of filters & Views) or deleted (rules).
• The Application used to manage the business also has Outlook integration which we've since turned off
• I deleted the user's Email profile in Control Panel Mail Applet and allowed the profile to recreate itself.
• If say fred@externalcompany.com sends Accounts@ourcompany.com an email it is not displayed in Olk for Accounts user.
• If Fred CC's admin@ourcompany.com, Admin can see the email but not Accounts.
• If Admin forwards the email from fred@externalcompany.com to Accounts@ourcompany.com the email does not show up in the list of email in the inbox

The departing employee may have left in unfavourable circumstances and may have used a lesser known technique that has outsmarted me.  Where or what should I check