RE7outlook.DLL is used to integrate Outlook and the Raiser's Edge.  The RE7Outlook.dll can be found via the following locations:

32-Bit Operating System:  C:\Program Files\Blackbaud\The Raisers Edge 7\DLL\RE7Outlook.dll
64-Bit Operating System:  C:\Program Files (x86)\Blackbaud\The Raisers Edge 7\DLL\RE7Outlook.dll