The best solution for resolving email quota issues is to create an email archive. This will allow you to move mail from a busy inbox to a local store to free up server space.
Select Tools from Outlook Toolbar and scroll to Account Settings...
Select the Date Files Tab.
Click on the Add... button.
Select Office Outlook Personal Folders File(.pst) .
Click the OK button.
Choose an appropriate location for your Personal Folder and name for the Archive.
D:\Data is the recommended file location.
It is recommended that the File name and the Name: be the same (excluding ".pst") this will make finding the mail archive easier for Tech support.
Click the Close Button to complete the process.
The Archive will be below your Mailbox
By Right Clicking on the name of the Archive you can select the option to Add New Folder to organize your mail.
To move mail click and drag mail from your inbox to your newly create mail archive.