To have your Mac OS X Mail remove messages from the server when you check mail (using POP), you will follow these steps:
- After opening the Apple Mail program, click on Mail from the menu at the top.
- Click on Preferences.
- Click on Accounts.
- If you have more than one mail account, select the one you want to work with.
- Click Advanced.
- Make sure the box next to Remove copy from server after retrieving a message is checked.
- You can also remove messages currently saved on the server by clicking the Remove now button.
- Click Save when you close the Preference pane.
Using Remove copy from server after retrieving a message will make sure your messages are always downloaded to your Mac, and prevent your mailbox quota from being exceeded.