Please find below the steps I followed: I copied the old profile from my Linux computer to my Macbook (OSX 10.9.5) into: /backupPath/oldID.default The same directory contains: /backupPath/profiles.ini I downloaded and started Thunderbird V- 45.6.0 I quit Thunderbird This results in the presence of the files: ~/Library/Thunderbird/newID.default ~/Library/Thunderbird/profiles.ini I edited the file: ~/Library/Thunderbird/profiles.ini which now reads as: [General] StartWithLastProfile=1 [Profile0] Name=default IsRelative=1 Path=/backupPath/oldID.default Default=1 I restart Thunderbird. And all is well, the account is there with apparently all messages with their content and their attachment. To be safe, I change some settings: In the account settings: in “Local Folders->Disc Space” I set: “Don’t delete any messages” In the Thunderbird preferences->Advanced, I unchecked the box: “Compact all folders when it will save over 20 MB in total” Once that is done all is still here, I quit thunderbird. BUT: when I restart Thunderbird, all my folders are empty. Additionaly, the size of the directory: /backupPath/oldID.default has been reduced by nearly half. Note that I don’t mind about saving the disc space. All that is done offline, so there is no relation to the actual email server. I repeated the above steps a few times (each time, I used the “full-sized” oldID.default which I copied on an external hard drive beforehand for safety) Is there something I do wrong? Actually, I am pretty sure there is something I do wrong but I have no clue what.