Situation: The use can’t search more than 6 months in his Outlook 2016.
Troubleshooting: 1. Make sure the Cache Exchange Mode is set to the years you want to search. To do that, go to File>Account Settings. Highlight the email account and click change.
2. It could be the computer problem. To test it, login office.com to do the same search. If you can search on office.com but Outlook. Try to repair Microsoft Office first.
3. It also could be the computer is old and slow. try another computer for a test.
