Windows 8 and Windows RT do not natively support the POP3 email protocol.
If you use Windows 8 or Windows RT you will need to use the IMAP protocol for your emails.
More details can be found on the Microsoft website at http://windows.microsoft.com/en-GB/windows-8/pop-email-accounts
Please note that when using IMAP, the email messages stored in your mailbox will count towards your disk space allowance.