Go here to setup your e-mail program automatically:
Email - MacMail - OS10 - Adding An Account (mac)
Open MacMail and click on Mail and choose Preferences.
Click on Add Account.
Type in your name, email address, pop3 and smtp settings(mail server is mail.yourdomainname.com), and the login info. For the username, use the complete email address.
Click Get Mail.
If you are unable to connect to the smtp server, your ISP may be blocking port 25 from 3rd party use. Contact your ISP if this occurs. You can also use mail.your-domain-name.com and SMTP Port 587.