Enabling Secure Connections in ThunderBird 52 and above
Instructions for ThunderBird 52 and above.
1- Open the Thunderbird application.
2- From the menu options, go to Tools->Account Settings.
3- Find the account labelled with your HIS-hosted email address on the left side panel and click on "Server Settings".
4- Under "Server Settings", look for the "Security Settings" section and change the pull down menu
Connection Security to "SSL/TLS")
5- Leave the Authentication method to "Normal Password"
6- The Port number should automatically have been changed to "993" for IMAP. (Note: If you are using POP instead it will automatically change to "995". Check this to confirm you made the correct setting change for "Connection Security".
7- Click "OK" to close the dialog.
8- Find the account labelled Outgoing Server (SMTP) on the left side panel.
9- In the list displayed, click on the SMTP server you use for your HIS-hosted Account, then Edit.
10- Look for the Security and Authentication, and change Connection Security to: SSL/TLS
Check that the port number has been changed to 465
11- Click "OK" to close the dialog.