30 Day Online Archive

I made some up for you.

Click on the gear icon in the upper right-hand corner:

This will open your Outlook Settings. Click on Retention Policies:

Click Add New Policy: you should see a list of available options to choose from, select the ITS 30 Day Archive

And hit save, this will automatically move all his emails from his mailbox to his online archive once they are 30 days old, which should really help with space management.