User Configuration > Administrative Templates > Microsoft Outlook 2016 > Account Settings > IMAP
User
HKCU\software\policies\microsoft\office\16.0\outlook\options\mail
When "purge on switch" is enabled, IMAP e-mail messages marked for deletion in the current folder will be permanently removed from the server when the user switches to another folder. This setting will allow you to enable the IMAP "purge on switch" feature.