How do I determine what version of Outlook I have in order to ensure I get the correct E2S4 version?
The simplest way to determine the version of your Outlook is through the Help section: go to Help menu, click About Microsoft Office Outlook and you'll see the version. Microsoft also created a page with all the major versions of Outlook that have been released along the time.
Microsoft Support website for Outlook versions: https://support.microsoft.com/en-us/kb/870929