User Configuration > Administrative Templates > Microsoft Outlook 2016 > Account Settings > Exchange > Cached Exchange Mode
User
HKCU\software\policies\microsoft\office\16.0\outlook\cached mode
This policy setting allows you to configure the amount (by date) of user email Outlook synchronizes locally using Cached Exchange Mode. If you enable this policy setting, you can specify the time-window of email messages that Outlook synchronizes to users' computers. The options you can select are: 3 days, 1 week, 2 weeks, 1 month, 3 months, 6 months, 1 year, 2 years, 3 years, 5 years, and All. If you disable or do not configure this policy setting, Outlook synchronizes the last 12 months of email messages to users' computers.