Thunderbird has an option to allow the welcome screen to be changed to a web page of the user’s choice. It can even be a web page stored locally on the hard drive. My Firefox home page is a file on my hard drive. I have links to sites I visit often, such as the sites I administer, or links to my webmail accounts.
On Windows use these steps to change the Thunderbird welcome screen:
click on Tools -> Options
click on Edit -> Preferences
The box labeled Location should contain something like: chrome://messenger/locale/start.html if it has not been changed previously. Click the button labeled Restore Default to undo any custom settings.