how to require a password to veiw emails each time

Hello, i was wondering if it is possible require a password in order to open a email from the inbox. currently i have Thunderbird set to require a password when i open the client, what i would like to do is have it require me to type in a password to read each email in the inbox. the reason for this is that the computer that i am using is used 90% of the time by myself but there are other people in the office that will need to use have access to the computer at times. one of my email address's contain important costing and invoice emails that i do not wish anyone else to be able to see. Normally i could just keep Thunderbird closed and only open it ( thus requiring a password) when i need it but this does not allow me to see when i receive a new email. Is it possible to keep thunderbird open so that i can receive the notice of a new invoice being received but when i try and open the email it requires me to put in my password at that time? Thank you,