Bill,
This should fix it if you are running 64 bit Outlook:
1) First, log into the workstation where you're seeing these email functionality issues in Dynamics SL 2015, as an Administrator account.
2) Go to Start > Run, type REGEDIT and click OK to open the Registry Editor
3) You will want to backup the HKEY_LOCAL_MACHINE keys by right-clicking on that node, selecting Export and saving the keys to a location you can restore from later if necessary
4) Once that is done you'll want to expand HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\IniFileMapping\win.ini
5) If you look in the right-hand pane when win.ini is highlighted you'll likely not see a MAIL string key. Right-click on win.ini and select New > String Value. Name this new value: MAIL
6) Double-click on the MAIL key and set its value to the following:
SYS:MICROSOFT\WINDOWS NT\CURRENTVERSION\MAIL
7) You then need to create the key(s) that the MAIL key refers to. If this is a 32-bit machine you'd need to use option A below. If this is 64-bit use option B:
Option A:
a) Expand HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion
b) Right-click on CurrentVersion and select New > Key
c) Name this new key: MAIL
d) Right-click on the new MAIL key and select New > String Value.
e) Name this new string value: MAPIX
f) Double-click on MAPIX and set the value to 1.
Option B:
a) Expand HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion
b) Right-click on CurrentVersion and select New > Key
c) Name this new key: MAIL
d) Right-click on the new MAIL key and select New > String Value.
e) Name this new string value: MAPIX
f) Double-click on MAPIX and set the value to 1.