1. Open Thunderbird Mail. From the Tools menu select Account Settings. The Account Settings box appears.
2. In the white area on the left, select the entry Outgoing Server (SMTP). The Outgoing Server (SMTP) Settings appear on the right.
3. In the “Server Name” box the entry should be smtp.gn.apc.org
4. Verify that the Use name and password box is ticked. Click on the box to tick it, if it is not ticked.
5. In the User Name box enter your user name, usually the bit before the “@” sign in your email address.
6. Click the OK button on the bottom. Authentication has now been enabled. Please note, you will be prompted for your password the first time that you send email. You can tick the box “Use Password Manager to remember the password” to avoid having to enter it every time that you send email.
Please follow the below document and make the changes, so that you can send the emails using Mozilla Thunderbird.