I'd suggest you move your entire profile. This contains your message store, address books and much else. If you were installing Thunderbird afresh on a new clean computer with an SSD for the OS, you'd hope the installation would be sensible enough to place user files on a regular HDD, in which case TB's profile would automatically be placed under ''Users'' (formerly ''Document and Settings'') and this situation wouldn't arise. Move your whole profile and you never have to worry again about email-related data accumulating on the system drive. https://support.mozilla.org/en-US/kb/profiles-tb You ''can'' move individual email storage locations, but I would urge you not to do this. It fragments your profile and makes ongoing management and maintenance of it much more difficult. Look under '''Tools|Account Settings|{select account}|Server Settings→Local Directory''' for where to set this, but again, I must advise you NOT to use this. Note that when you import email data from another email client, it arrives in Thunderbird under its Local Folders "special account", so that is specifically where you need to go in Thunderbird to move its mail store to another drive. If you're really tight on space on C, move the profile ''before'' importing. ;-) No menus? http://chrisramsden.vfast.co.uk/13_Menus_in_Thunderbird.html Also: http://www.chrisramsden.vfast.co.uk/11_Thunderbird_Settings_and_the_Profile.html