To set up Thunderbird (or SeaMonkey) to use authentication with your SMTP server:
- Go to “Tools -> Account Settings -> Outgoing Server (SMTP)”.
(If using SeaMonkey: go to “Edit -> Mail & Newsgroup Account Settings -> Outgoing Server (SMTP)”.)
- Select the server and press the Edit… button.
- Check the “Use name and password” option.
- Add your username. Your username might be your full e-mail address (e.g., “email@example.com“) or only the part before the “@” (“johndoe”), depending on your service provider; check with them which is correct.
- Click “OK”.
Thunderbird will ask you for your password the first time you send email and you can optionally save it at that time.