If you’re like most people, you probably use a mail client (Microsoft Outlook, Mozilla Thunderbird, Eudora, MacMail) to download your email from a POP server. By default, most mail clients download a copy of the mail message, and then instruct the server to delete the original message.
This is essential so that mail does not pile up on the server. However, it can be problematic when you want to check your email from several devices, like a home computer, a work computer, and a mobile phone or PDA.
You can accomplish this by enabling an option called: Leave a copy of the message on the server. Like it says, when you enable this option, it will not delete your mail from the server upon downloading it. However, if you enable this option on all of your devices, your messages will never be deleted. You should probably leave one device without this option so that the messages will eventually be deleted.
Alternatively, you can usually specify a specific number of days before mail is deleted. If you allow yourself a one-day buffer period, you should be able to download your mail onto many devices without worrying about using up all your storage space.
This option should be somewhere in the advanced area for server settings. A quick help search to leave a copy of the message on the server should get you the specific instructions for your mail client.