Office 365 – Enable In-Place Archiving – Warning: The user hasn’t logged on to mailbox ‘name’.

Attempted to enable Archiving for one mailbox in O365 Exchange Center, but I kept receiving a Warning message when going into ‘View Details’ after enabling the account.

I needed to query the last logon time for the mailboxes to confirm there was a last logon:

Then, I needed to enable the mailbox with PowerShell.

In order to start emails syncing to the Archive mailbox, it can take up to 24 hours to initialize. We need to run an additional command to get the mailboxes syncing: