User Configuration > Administrative Templates > Microsoft Outlook 2016 > Account Settings > Exchange
User
HKCU\software\policies\microsoft\exchange
This policy setting allows you to set the maximum number of Exchange accounts allowed per Outlook profile. If you enable this policy setting, you will be able to set the maximum number of Exchange accounts allowed per Outlook profile. If you disable or do not configure this policy setting, the default maximum number of Exchange accounts allowed per Outlook profile is 10.