1. From the menu bar, choose Tools then select Accounts.
2. In the Internet Accounts window, click on the Mail tab. Select the account that you wish to change and click on Properties.

3. Click on the Servers tab.
4. In the Incoming mail (IMAP) field enter your IMAP host (imap4.yourdomain.com).
5. In the Outgoing mail (SMTP) field enter your SMTP server (smtp.yourdomain.com) and click Next.
6. Enter your full eMail address in the Account name field.
7. Check "My server requires authentication" under the Outgoing Mail Server heading.