Hi Mary,
Thank you for posting the query in Microsoft Community Forums.
By setting the server to a POP3 server, you can set Mail to access your email from MSN.
Step 1: Open Mail and select "Preferences from the "Mail" menu.
Step 2: Click "Accounts" and click on the plus sign under "Accounts" to begin adding a new account to Mail.
Step 3: Type your MSN email in the "Email Address" text box and your password in the "Password" text box.
Step 4: Click "Create" and Mail will attempt to automatically apply the necessary settings for your MSN account. Click "Create" on the "Account Summary" page to finish creating your MSN account in Mail.
Also refer:
https://discussions.apple.com/thread/5723157
Hope this information helps.