hi boitel, I think your are asking whether Thunderbird ("TB") keeps or removes "data" when TB is re-installed. TD saves personal information such as messages, passwords and user preferences in a set of files called a "profile", which is stored in a separate location from the Thunderbird program files, and is not destroyed when TB is re-installed. You may actually have more than one profile. It's safe to re-install TB, but if you wish to be cautious, then backup your data. Data/Profiles can be found in Menu -> Help -> Troubleshooting Information -> Profile Directory -> Click on "Open Directory", this is the directory and probably names "someting-default" (see also below Support Article where you can find a note on the Windows folder where your Profile/Data should be located). TB should open with the default Profile once re-installed. See also Support Article [[If I reinstall T-Bird do I lose my old e-mails]] and [[Updating Thunderbird]] (states "Simply download and install the latest version from the Thunderbird website, and Thunderbird will pick up your existing data.) As as side note, if you have server type IMAP, then you will still have emails on your server (provided you have not deleted emails and emptied Trash), and these will be downloaded again to your local drive once you set up the account again. All the best from Stockholm.