Could you check Use auto-complete list to suggest names when typing ... is checked under FIle Options - Mail Tab?
Refer this link:
https://support.microsoft.com/en-sg/help/2682333/autocomplete-not-working-correctly-in-outlook-2010
ASKER
Dear MAS,
I have tried disabling all the Outlook Addins but this has not helped.
Dear Kesavan,
This setting is enabled by default and despite it being checked, the cache is not being retained.
Further assistance shall be appreciated.
Microsoft Outlook is a personal information manager from Microsoft, available as a part of the Microsoft Office suite. Although often used mainly as an email application, it also includes a calendar, task manager, contact manager, note-taker, journal, and web browser.
TRUSTED BY
If yes please remove it and configure a new outlook profile and try.