The file itself is quite big 14GB in zip format.

How did you create the backup in the first place, using what software?

after unzipping files they have strange formats.

What software did you use to unzip? What exactly does 'strange format' mean?

Typically anti-virus software is struggling when dealing large files. Turn it off when unzipping the archive. If your zipped archive got corrupted then there's nothing you can do anyway.

I tried installing Thunderbird and importing ZIP file but it doesn't work.

I don't understand what you were trying to achieve. Thunderbird cannot import a zip file. What you want is to restore your Thunderbird profile folder from the backup, and then tell Thunderbird to use the restored profile folder. There is nothing to import.

Hey christ,

I was trying to save 8 years of data from my thunderbird and copy it on the external drive. It has been several months ago if I am not mistaken I couldn’t make a transfer to a disc as the size was 24 GB therefore it had to be packed.

As far as I remember the process took ages but went smooth. Now after 4 months I would like to get back access to the files but when I unpack the folder the files seem to be of unknown format. I tried downloading thunderbird + and open files but it is not possible.

I would like to get back access to the files but when I unpack the folder the files seem to be of unknown format.

Before anything else, you'll have to solve this problem first. Once you've successfully restored your profile backup people here will be able to assists in case there are any further questions.