Enable Auto Archive in Outlook

An additional "Online Archive" mailbox will appear automatically in your Outlook.

Mailbox selection pane

 

To enable archiving, right-click a folder or mailbox you'd like to set up archiving for. Then select Properties.

 

Go to the Policy tab, under the Online Archive section, assign the policy you'd like and then click OK.

 

Note
It can take 24 hours before the archiving job runs. You likely wont see the archiving start right away.