To setup an email account with Thunderbird:

1. Launch Thunderbird.
2. Select Tools from the top menu bar and click Account Settings.

tools-account-settings

3. From Account Actions select Add Mail Account.

add-mail-account

4. Enter your email account details.

mail-account-setup

5. Thunderbird will automatically search for mail server settings. A green light indicates that the search was successful. Click Edit.

mail-server-settings

6. Click Manual Setup:

Server Name: mail.yourdomain.com [Port 110].
User Name :The email address you are sending email from.

Ensure that the Use secure authentication check box is NOT ticked.

manual-setup

7. Click Outgoing server (SMTP) in the menu on the left hand side.

outgoing-server

8. Ensure that your Server Name is smtp.yourdomain.com and that the Port is set to 587.