The recipients of email messages that are sent programmatically in Outlook 2013 aren't added to the users nickname cache. Therefore, when you try to send an email message to the same recipients manually, you won't get any suggestion for those recipients' names. This update enables you to turn on the ability for recipients to be added to the nickname cache when email messages are sent programmatically. To change the behavior, install the MS16-099: Description of the security update for Outlook 2013: August 9, 2016, and then follow these steps.
Important Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.
Exit all Microsoft Office applications.
Start Registry Editor:
In Windows 10, go to Start, enter regedit in the Search Windows box, and then select regedit.exe in the search results.
In Windows 8 or Windows 8.1, move your mouse to the upper-right corner, click Search, type regedit in the search text box, and then click regedit.exe in the search results.
In Windows 7 or Windows Vista, click Start, type regedit in the Search programs and files text box, and then click regedit.exe in the search results.
Locate and then select the following registry subkey: