Seemingly, Windows 8 does not support POP3. AFAIK, a fundamental difference between POP3 and IMAP is that with POP3 you are expected to download the emails to your PC for storage (although many ISPs nowadays have the ability to also leave copies of emails on their servers). Whereas with IMAP it is the other way round - their servers are viewed as the prime storage and downloads to your PC are considered transient.
Basically, MS and Windows are taking a Cloud based approach.
The workaround that some sites are suggesting it to open an account with someone else that is supported by Windowsa 8 mail (e.g. outlook.com, gmail) and forward all of your email to them for collection by your Windows 8 email. See click here or here Not very elegant or clever at all.
The alternative is to install a 3rd party email client that does support POP3 as one of the above links suggests.