Hi Did you follow the instructions for moving Thunderbird to a new computer or location? The page will customize for the OS you are using, it explains where to find your Profile which is where address books and saved mail are stored. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data Thunderbird needs to access the contents of Profile and there are several ways to point Thunderbird to the original profile or move the contents to the current Profile. However, make sure to move from and to the same version of Thunderbird - it is not advisable to upgrade Thunderbird at the same time.