QUOTE(Tarun @ May 11 2005, 02:08 PM)
It may be an extension i'll look it up.
I think i found it.
(from the help on thunderbird)
Password protect the message pane (IMAP only)
With this trick, Mozilla Thunderbird will password protect the message list pane (aka the thread pane) by keeping it blank until you log in and enter a password for that account.
// Password protect the message list pane
user_pref("mail.password_protect_local_cache", true);