Thunderbird email (where IMAP or POP) still downloads the subject lines (at minimum) into a local database. This is a potential security threat if the laptop falls into unfriendly hands.
Solution : Move local data store into a directory protected by EncFS
The following assumes that you can find the data store under the server name in the appropriate profile under the .thunderbird directory (and that ~/Fieldstone is the name of a directory mounted by EncFS, and so hidden if the 'unfriendly' doesn't know the password) :
ls -l .thunderbird/8n9uvc7r.default/ImapMail/imap.mail.fieldstone cd .thunderbird/8n9uvc7r.default/ImapMail/ mv imap.mail.fieldstone ~/Fieldstone/ ln -s ~/Fieldstone/imap.mail.fieldstone