There are basically two different types of e-mail account. In the case of a "POP3" e-mail account, the messages are retrieved from the server and deleted from the server in the process. This means, for example, that you can no longer access these e-mails from a second computer. In the case of IMAP mailboxes, the e-mail messages are not deleted, but, instead, copies of them are stored in your e-mail program. You can link several e-mail programs with the mailbox. Changes are then replicated in every e-mail program and you can retrieve your e-mail messages as often as you wish.