This document explains how to enable SMTP Authentication for the Macintosh OS X MAIL email client.
Enabling SMTP authentication

1. Open MAIL.

2. From the MAIL menu, select Preferences. Select the Accounts icon and click on your email account under the Description heading. Click on the Edit button on the right. The Account Information appears.

3. If you have OS X 10.10 or later, select the “Advanced” tab. If the top setting is “Automatically detect and maintain account settings” and that is ticked, untick it and then close the Preferences box. Click “Yes” in answer to saving the settings (it may prompt for your GreenNet password), and then reopen the Preferences box.

4. In the Outgoing Mail Server section, click on the double arrows and select Add Server. from the menu. The SMTP Server Options box appears.

5. In the Outgoing Mail Server box, enter smtp.gn.apc.org

6. In the Authentication box, click on the double arrows and select Password.

7. In the User Name box, enter your username (username@gn.apc.org – not the full address, just the username). In the Password box, enter your password for this email address.

8. “Use default ports” and “Use Secure Sockets Layer (SSL)” should both be selected.

9. Click OK to return to the Account information page. In Outgoing Mail Server section, click on the double arrows and select smtp.gn.apc.org . Note that it will have your email address listed

8. The Outgoing Mail Server entry should now show smtp.gn.apc.org followed by your email address.

9. Click OK to close and then close the Accounts box by clicking the red button. SMTP authentication has been enabled.

See also http://www.gn.apc.org/support/i-am-receiving-email-fin...