These instructions are only relevant to POP3 Accounts
To Manage leaving copies of messages on the server using Office Outlook 365
Click Account Settings->Manage Profiles
Click the Email Accounts Button
Double click your email address
Click the More Settings Button
Click the Advanced Tab
Locate the Delivery Heading
To Disable leaving a copy of messages on the server
Untick Leave a copy of messages on the server
To clear mail from the server at regular intervals
Tick leave a copy of messages on the server
Tick remove from server after after x amount of days via the dropdrown box containing the days option e.g 7 days etc
Untick remove from server when deleted from 'Deleted Items'
Now check for new email, this will clear mail stored on the server.