You see no suggestions for recipient names when you try to send email messages to some recipients in Microsoft Outlook 2016. This issue occurs after an email message is sent programmatically to the same recipients in Outlook 2016. By default, recipients of an email message aren't added to the nickname cache when the email message is sent programmatically. To change the behavior, install the MS16-107: Description of the security update for Outlook 2016: September 13, 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: