I need to keep certain emails private for only my viewing (kids). I have a folder called Private. Can I require a pw to open it?

Question

Certain emails are for my eyes only. I put them in a local folder called "private." How can I prevent other users from opening that folder either accidentally or on purpose.

Answer 1

I think a much better approach would be to password protect your User account in the Operating System, and set up another account or accounts for the children. You limit their rights to stop them installing ad-hoc and wrecking the computer. You set up a screensaver with password to lock your account when not at the computer.
This add-on: https://nic-nac-project.org/~kaosmos/profilepassword-en.html lets you password protect your Thunderbird profile, though it is a weak form of protection. OK for very young children, but older kids will likely see it as a challenge to hack it.
See these:
http://kb.mozillazine.org/Protecting_the_contents_of_the_profile_-_mail
And note "Note: You can password protect the contents of the message pane by setting mail.password_protect_local_cache to true using the configuration editor in conjunction with setting a master password in Thunderbird." listed under "medium methods".
…but I'm not sure how you'd lock the pane once you'd unlocked it. You'd probably have to close Thunderbird, so it challenges the user when next run.
As mentioned in the article and the webpage for the add-on, none of these measures guard against your email being stored in plain text and thus visible to anyone browsing the file system. Therefore your best option is to use User Accounts, with logins and passwords, and control access to your own data that way. A user would need admin ("root") privileges to access your data, or be sufficiently knowledgeable to be able to boot with a linux CD or similar.
Storing your email data on a USB stick that you can take away with you.
All of the above require some diligence and vigilance on your part, as you must remeber to lock or close Thunderbird, or logout, or remove the USB device before you leave the computer. A password-protected screen saver and separate User Accounts in the OS provide the closest to an automated protection system.