Check your mail server settings
  1. On the Tools menu, click Accounts.

  2. Click the mail server, and then click Properties.

  3. On the Servers and Advanced tabs, check the settings against those given to you by your Internet service provider (ISP).

    If everything matches, contact your ISP to verify that you have the correct settings and that their servers are operating correctly. Also, make sure your ISP server supports PPP, SMTP, and POP3 protocols.

If this did not fix the problem, try checking your ISP connection.