If you have a POP email account, messages sent to you are stored on Post Office Protocol (POP) servers at your Internet service provider until you connect and retrieve them. When you connect to your POP email account, the messages are downloaded to your computer. The messages remain on the mail server unless you specify that they should be removed. To do so, choose the Advanced pane of Mail Accounts preferences and then either click "Remove now" or select "Remove copy from server after retrieving a message" and indicate when to remove them using the pop-up menu.

POP is the most common method of accessing email, but if you use multiple computers to read your mail, you might find an Internet Messaging Access Protocol (IMAP) account more convenient. Ask your Internet service provider (ISP) if IMAP mail is available for your account. With an IMAP account, you can keep your mail on your ISP's server, so you can access it again from any computer.