Depends upon how you have set this up. Usually, if different people use the same computer, each person is issued with their own User Account which they log into using a password of their choice and then they start thunderbird. Then each users Thunderbird profile folder and mail account is kept in each User Account. This means that no one can access personal mail of another person without logging on to their User Account. It also prevents the issue of opening wrong Profile. But if you are all using a common User Account and Thunderbird has been set up to contain different Profiles each with own mail account, one per person, then you need to have the Profile Manager open prior to Thunderbird lauching so that the correct Profile can be opened on demand. Profile Manager: http://kb.mozillazine.org/Profile_Manager There will be a check box 'Don't ask at startup' you need to remove the check - deselect that option to force Profile Manager to ask at startup. then you can select the desired Profile and click on 'Start thunderbird'. This method is not so secure as anyone can access any Profile and read downloaded emails. If using this method it is advisable to never store any passwords as they can also be seen by others or use the Master Password setup to at least prevent other users from seeing stored passwords. http://kb.mozillazine.org/Master_password