You can set new locations in Thunderbird. Each account has a box named ''Local Directory'' (under Server Settings) which sets the location of the message store. I'd work by copying the data files from your profile to the new location, then in Thunderbird using the browse button to find and enter its new location. But rather than picking out individual message stores, I'd look at moving the whole profile. Move the data part of your profile and change ''profiles.ini'' to suit. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data The problem with both of these approaches is that there is a risk that every time you plug in your SD card or an external HDD, it will take a drive letter different from the one you used last time, and then so the settings in ''Local Directory'' or ''profiles.ini'' won't be able to find them. If you have a permanently attached internal real spinning metal HDD then use that if possible. If you are obliged to use a portable pluggable device then you might do better to install Portable Thunderbird onto it and move your old profile's data over on to it.