Answer

PROBLEM

Microsoft Exchange Information Store does not start after GFI MailSecurity or MailEssentials has been remioeved.

ENVIRONMENT

• GFI MailEssentials
• Microsoft Exchange 

SOLUTION

1. Navigate to the registry key below and make sure to change the value from 1 to 0:
   • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\VirusScan\Enabled key to "0" 
2. Restart IIS Admin / Transport role
3. Try opening Microsoft Exchange again

CAUSE

Microsoft Exchange server is still trying to find an information store scanner which was removed during the removal of GFI MailEssentials / GFI MailSecurity. The registry key still shows as if it was available.