Open your Thunderbird profile folder, QUIT Thundebird and copy the mbox file to Mail > Local Folders. Remove the .mbox extension, it's not needed, then launch Thunderbird. You will find the messages under the Local Folders account.

Great! Thanks so much for your help!!! Have a good weekend :)

I tried this with Thunderbird 78.5.0 on Ubuntu 20.04, but it did not work. Any other suggestions? Thanks.

I tried this with Thunderbird 78.5.0 on Ubuntu 20.04, but it did not work. Any other suggestions?

What exactly did you do, step by step?

Hello! I did the same as rmorain, transfering a WORK.mbox created on Catalina Mail on Mac to THB 78.5.2

The procedure does not work either and I followed exactly the steps outlined by Stans.

I get the following status from my local folder (see the joined picture). No messages appear! It seems the transfer of messages is not done at all...

Thank's a lot for advices, Daniel.

"Open your Thunderbird profile folder, QUIT Thundebird and copy the mbox file to Mail > Local Folders. Remove the .mbox extension, it's not needed, then launch Thunderbird. You will find the messages under the Local Folders account."

I have a mail box named WORK that I want to transfer on my fresh TB 78.5.1 installation containing 3 IMAP accounts.

Now, I want to transfer a personnal mailbox named WORK on TB. When I ask Mail to export the mailbox, it create a file WORK.mbox (4Ko) AND a (huge, 3.5Go) folder named WORK containing everything.

So, WHAT SHOULD I DO, please ? Put the WORK.mbox file in the Local Folders ? What about the huge WORK folder ?

Thank's for your help, Daniel.

The huge file is the one you want.

Thank you but it doesn't work... I have put the huge file in the Local Folders, but when I open TB, it does show the WORK folder and its subfolder (CPT) but no message appear (see pict). Also, the subfolder CPT contains many subfolders that do not appear. It seems nothing is imported... Is there any synchronisation to be done ? Shall I try an older version of TB ?

I'm really stuck and yet I'd like to install TB on my mac because Catalina's Mail application is a real disaster!

Have a nice day and thank's for help. Daniel.

Well, now it seems very clear to me that the proposed solution might work with outlook or other client but when coming (freshly) from Apple Mail on catalina, it simply doesn't. It's may be related to the export format of malboxes from Mail catalina ? I don't know... It's a pity because Mail on catalina is a real catstrophy. Have a nice day. Best. Daniel.

You may have better luck using the Import Export Tools NG add-on to import the mbox file.

I have already used the Import Export Tools NG add-on. When I export a mailbox file from Apple Mail, it create a .mbox file (few Ko only) and a huge folder. It doesn't work with Export Tools NG add-on because it says to import the .mbox file but nothing happens and it is really very poorly documented... In fact, beacause of that, I don't really know how to proceed with the Import Export tool... It's really very frustrating beacause Apple Mail on Catalina is a nightmare... Best, Daniel.

You must be choosing the wrong file. I just tried copying the mbox files (exported mailboxes from Apple Mail on High Sierra) to Local Folders and they loaded just fine. The mbox file that you should be copying is simply named "mbox" without any file extension.

For example, in my test scenario, I have a folder called 2020 under the Archives mailbox in Apple Mail. When I right-click the 2020 folder and export it (mailbox) to my Downloads folder, a folder named Archives is created. Inside it, an archive file of sorts (type is Mail Mailbox) called 2020.mbox is found, inside which there is a file called "mbox" and another called "table_of_contents". Both files have no extension, but the mbox file is huge and it's the one containing messages. I copied that mbox file to Local Folders and renamed it to 2020 and when Thunderbird loaded, a folder named 2020 was found under the Local Folders account and it contained the messages.

Thank you for your help Stans but now I see the difference with your export on Sierra.

Suppose I want to export a mailbox called WORK in Apple Mail to TB (like your 2020 folder). When I export it (including subdirectories), I get what you see in the attached image. Here, you see that the WORK.mbox folder is only 36 bytes and the mbox file inside is 0 KB, which seems normal to me because my WORK folder does not contain any messages at level 0 but it contains several subdirectories of total size 3,45Gb. So here, I already have a difference with your case since in your case, the 2020.mbox file is large whereas it is only 36 bytes in my case...

Then, I made several attempts :

1) If I put the huge WORK folder in the Local Folders directory of my profile, nothing appears in TB, only empty boxes... Same thing if I put both the WORK.mbox file with the huge WORK folder in the Local Folders directory of my profile. (I then erased everyting).

2) If I create a subfolder WORK in my Local Folders directory in TB and I import all the subfolders of the huge WORK folder, the all hirarchy of the WORK folder is imported but all imported sudirectories are empty. (I again erased everyting).

3) But now, if I right click on the WORK sub-folder I created in my Local folders in TB, ask to import mailboxes and select the method: "choose a folder where to look for the Mbox files to import (including sub-folders)" then it will correctly import the sub-folders BUT without the correct names (see the second attached picture). So it seems that this option works but the names of the sub-folders are not correctly transcribed. That's where I'm at and even if it seems close to the solution, I don't know how to get the correct names of subfolders. Doing it by hand (I don't know whether it's possible) would take me hours with all other mailboxes I have to import...

Your suggestions are again very welcome and I thank you again for your help! I would so much like to leave Mail under Catalina which is a real disaster and TB is exactly what I need!

Daniel.

3) But now, if I right click on the WORK sub-folder I created in my Local folders in TB, ask to import mailboxes and select the method: "choose a folder where to look for the Mbox files to import (including sub-folders)" then it will correctly import the sub-folders BUT without the correct names (see the second attached picture). So it seems that this option works but the names of the sub-folders are not correctly transcribed. That's where I'm at and even if it seems close to the solution, I don't know how to get the correct names of subfolders. Doing it by hand (I don't know whether it's possible) would take me hours with all other mailboxes I have to import...

This would be the best approach, but as you can see, each imported mbox file does not bear the name of the PARENT.mbox mailbox folder. The Import Export Tools NG add-on is NOT going to inherit the name of the PARENT.mbox mailbox folder when importing the mbox files they contain. It will only inherit the name of the actual mbox file itself (the files called mbox without any extensions). This means, you have to rename each mbox file from "mbox" to the name with which it should appear in Thunderbird. For example, inside the LAB.mbox parent folder, there is a file named mbox. Rename this file from "mbox" to LAB and it will be imported with the LAB name. Granted, it's going to be a lot of work to do by hand, but that's the only way you will get them to appear in Thunderbird with their corresponding Apple Mail names.

You may be able to batch rename each mbox file to the correct name using a script or command line via the Terminal. I am not familiar with the macOS Terminal enough to craft a command line that you could use, but I'm sure it can be done. For example, if you exported the mailboxes to your Downloads folder, the script would work as follows:

Look for a file called "mbox" inside the Downloads folder and all subfolders (recursively), and for each found file, take the "PARENT.mbox" name of the folder/path inside which the mbox file was found, strip the ".mbox" bit from it and apply the remaining "PARENT" bit to the found mbox file. You may get better help with accomplishing that here https://discussions.apple.com/communi.../mac_os. Once each mbox file is appropriately named, you can then import them in one go using the "choose a folder where to look for the Mbox files to import (including sub-folders)" option.

I found this https://askubuntu.com/questions/746860/rename-a-file-to-parent-directorys-name-in-terminal

Thank's a lot Stans, I am going to experiment with a script, shouldn't be too hard. I'll let you know.

Best, Daniel.

Hey, I'm having this problem too -- is anyone still around to help? I've moved the mbox files from Apple Mail into the Profiles/Mail/Local Folders of Thunderbird, but I can't see my individual messages in the mail viewer window. I was going to try the option (listed above) of choosing "a folder where to look for the Mbox files to import (including sub-folders)" but this option doesn't appear for me when I right-click the subfolder in Thunderbird. What am I doing wrong? Thanks, Chris Lotito

Hey, I'm having this problem too -- is anyone still around to help? I've moved the mbox files from Apple Mail into the Profiles/Mail/Local Folders of Thunderbird, but I can't see my individual messages in the mail viewer window. I was going to try the option (listed above) of choosing "a folder where to look for the Mbox files to import (including sub-folders)" but this option doesn't appear for me when I right-click the subfolder in Thunderbird. What am I doing wrong? Thanks, Chris Lotito

You're missing the Import Export Tools NG add-on. It's what gives you the "a folder where to look for the Mbox files to import (including sub-folders)" option. Read through this thread again keenly. For help with installing an add-on, see Installing an Add-on in Thunderbird

Hey, I'm having this problem too -- is anyone still around to help? I've moved the mbox files from Apple Mail into the Profiles/Mail/Local Folders of Thunderbird, but I can't see my individual messages in the mail viewer window. I was going to try the option (listed above) of choosing "a folder where to look for the Mbox files to import (including sub-folders)" but this option doesn't appear for me when I right-click the subfolder in Thunderbird. What am I doing wrong? Thanks, Chris Lotito

Importing '.mbox' files from Apple Mail requires a bit more care, as the actual mbox that can be imported to TB is inside the .mbox folder exported from Mail:

http://forums.mozillazine.org/viewtopic.php?p=14069759#p14069759

Hi there, Apologies for my ignorance if this has already been covered, but I'm trying to solve the problem of importing my massive .mbox file into TB. Have read through the answers above but don't think anything covers this. I've done all the add ons and various recommended methods, but every time I get to my LaCie drive where my file is saved, TB crashes. If I go the other way, through account settings - message storage - local directory - browse, I'm unable to select my .mbox folder to upload (it's faint grey). Have taken screen grabs to explain where I get stuck. Cheers