The Mail app doesn't support POP (Post Office Protocol) accounts. To set up a POP account, other options are available from Microsoft.
From the Start screen, tap or click Mail.
Utilize the touchscreen (if available) or mouse to select on-screen options.
If not available, do one of the following:
Swipe up (starting from the middle of the screen) to display the Apps screen then tap Mail.
Click the Down arrow icon (located in the lower-left) to display the Apps screen then click Mail.
From the right edge of the screen, swipe left to display the charms menu.
If using a mouse, move the pointer to the upper or lower-right corner of the Start screen then move up/down.
Alternatively, press the Windows+C keys ( +C) located on the physical keyboard (if available).
Select Add an account.
Select Other account.
Select IMAP then select Connect (located in the lower-right).
Selected when a radio dot is present.
Enter the appropriate email address and password then select Show more details (located below the password field).
Enter the appropriate info (e.g. Username, Incoming email server, Port, Outgoing email server, etc.) then select Connect.
If you're not sure what your server info is, here are some common personal email server addresses. Contact your email provider if additional assistance is needed or your server info isn't listed.