Password is not protecting access to e-mail
If I press cancel twice on the password prompt I can then see e-mail.
Related: How can I block the view of even the message list until the password is entered? I want to have Thunderbird open on a page like Local Folders, not my last open view.
Alla svar (1)
This question comes up frequently. A Master Password in Thunderbird is not meant to protect your mailbox content from viewing, but only from accessing stored server passwords for sending and receiving that you don’t want others to view.
If you want to protect your Inbox from other people using your computer, let them use a guest account in Windows. Even if you could protect the mailbox content, any user that has access to your system can access its mail folders.
As for opening Thunderbird and having it set to select a specific folder, you could try the solution with the -mail startup parameter mentioned here. Note that the add-ons mentioned there no longer appear to be maintained or work, but there may be others that are/do.