I want to migrate/copy my Thunderbird from Windows 7 to Ubuntu, where I already set up another Thunderbird installation with some old and also some new accounts. To save me more configuration work, is it possible to just merge/synchronize the account settings and address books, so that the one on Ubuntu contains everything?

I have read access to the drive where Windows-Thunderbird is installed. However, I can't just copy old files and replace my current ones, as there are already other, new accounts set up I also need to keep.

Note that many of the accounts are POP3, so mails are saved on the disk, not in the cloud. I should copy them over too.

So in short: How do I merge and synchronize accounts created with Thunderbird easily?

  • You can either merge the text based files together then copy the emails to the apppropriate folder?
    – Ramhound
    Jul 1, 2015 at 18:31
  • I reworded my question to make it more clear. Jul 1, 2015 at 18:41
  • @Ramhound Could you go a bit more into detail please? Which files? Can I just append one to the other? What settings/data can I merge this way, where do I need another method? Jul 1, 2015 at 18:42
  • I have not used Thunderbird in years, stopped because of the incredible amount of work it takes, to export emails from Thunderbird. Your account settings are text files are they not? You should be able to merge the two files together ( keeping a backup of the originals ) and then manually transfer the existing physical .eml files over.
    – Ramhound
    Jul 1, 2015 at 19:06
  • @Ramhound And which file would that be? I can't find any file that is obviously named... Especially none of the plain-text files. Jul 1, 2015 at 19:23

1 Answer 1


The account details are all stored in the configuration data, which are saved in the text file prefs.js in the profile directory, so you can import parts of this from one system to another.

The relevant settings are the mail.account... and the mail.server... entries, but it is not as straightforward as copying and pasting.

  • You first need to extract the server settings (mail.server...) from the system where they are defined.
  • You then need to offset the sequence numbers so that they continue the sequence in the target system.
  • You can now merge the entries into the target prefs.js.
  • You next need to add mail.account.accountNN entries for the imported accounts.
  • If there were mail.account.accountNN.identities in the source prefs.js, then both they and the corresponding mail.identity.id... entries will need to be extracted, renumbered and merged.
  • You will need to add the new accounts to the mail.accountmanager.accounts entry and update mail.account.lastKey.

I think that is all that needs doing. Whether it is less work than entering the new accounts by hand will depend on the number involved.

I hope it goes without saying that both prefs.js files should be backed up first, and that Thunderbird should not be running while the files are being modified.

  • Thanks, this looks ok. I will try it, but I fear reentering all data is probably still easier and faster than this... :-/ Jul 3, 2015 at 6:59
  • I tried a fresh install and only copying pref.js . When I start thunderbird, all the account are there but I am asked for the password for each account. Any idea which other file(s) I have so that I don't have to enter the password? Thanks!
    – MagTun
    Aug 7, 2021 at 14:18
  • I have also tried copying pref.js and logins.json but I am also asked for the logins.
    – MagTun
    Aug 7, 2021 at 14:23
  • The solution is to also copy ` key4.db`. The full answer is here: superuser.com/a/1668072/300121
    – MagTun
    Aug 7, 2021 at 14:29

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