1. Launch the Exchange Admin Center (EAC)
Click on the start button and expand Microsoft Exchange 2016 and click on Exchange Admin Center.
2. Login
Enter your credentials to login.
3. Click on Recipients
Click on Recipients on the left and then mailboxes on the right.
4. Select a mailbox
Click on a mailbox that you want to enable archiving.
5. Click the enable button
On the user properties on the right hand side, click the enable button under archive.