On the menu bar click Mail, then Preferences, then Accounts and finally click the plus at the bottom right.

General Information 

Account Type: POP or IMAP 

Account Description: A personal description for your mail box 

Full Name: Your Name 

Email Address: The email address you created 

Click Continue 

Incoming Mail Server 

Incoming Mail Server: mail.yourdomain 

Username: your email address 

Password: mailbox password 

Click Continue 

Outgoing Mail Server 

Outgoing Mail Server: mail.yourdomain 

User Authentication - ticked 

Username: your email address 

Password: your mailbox password 

Click Continue 

Account Summary 

Check your settings 

Click Continue if you are happy with them. 

Click Done