Importing mail from Opera to Thunderbird

Martin Brinkmann
Sep 28, 2006
Updated • Mar 14, 2014
Email, Thunderbird

I finally decided to make the switch from Opera's M2 mail client to Thunderbird. The reason for the change was primary that the anti-spam combination Opera and Spamahilator was not working that well anymore, and I thought that it would be better to use a single program that handles both emails and spam detection.

Thunderbird has a great working junk filter that seems to handle spam really well even after just a few days of working with the program.

Importing mail from Opera to Thunderbird was not that easy. Thunderbird's imports feature is only working for imports from Outlook, Outlook Express, Eudora and Communicator which meant I had to find a way to import the mails manually.

To do that I had to first export the mail using Opera's mail client which thankfully is easy: right click a mailbox, select export and save the file. I did that to my received and my sent items folder but you can do this as well for the trash for instance or other folders.


The files have the extension .mbs and not very surprisingly Thunderbird uses this format as well to store mails. What you will have to do now is to create at least one email account in Thunderbird, you do that by clicking on Tools > Account Settings and then Add Account. Once added you see the path to the mails of that account in the account settings tab. I suggest you use one global setting for all accounts instead of different settings for each, this makes it easier to import the mails.

Navigate to the path that is mentioned in the account settings, it is usually something like

C:\Documents and Settings\[username]\Application Data\Thunderbird\Profiles\[random].default\Mail\Local Folders

Once there you notice many files in that folder like Inbox, Inbox.msf, Trash, Trash.msf and so forth. We will leave the .msf files unchanged and take a closer look at the files without extension. This is where Thunderbird stores our mails, the only thing we have to do is replace those files with our exported ones from Opera.

Which means that Received.mbs replaces Inbox and Sent.mbs replaces Sent. Do this for all folders that you have, simply remove the extension from custom folders and move them into that dir as well.

Thunderbird will import the mails at the next start and you should see all your mails just like in Opera.

Note that you should do this only with a new account as you will overwrite existing emails otherwise.


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  1. Kapil said on September 18, 2017 at 1:49 pm

    Hi, Do I have to re-create all folders ? … I mean, can I do if I’ve to only import ‘sent’ folder …
    Secondly, the folder here has different file names such as Received is Inbox in Mozilla.

  2. Moikie said on December 5, 2013 at 5:57 pm

    this procedure doesn’t maintain the sub-folder structure that I use in Opera Mail — I would have to go through four levels of sub-folders and export them individually …? That’s quite a few dozen of export-import / drag-and-drop operations. Or is there something here that I don’t understand.?

  3. Misterfish said on July 25, 2013 at 10:49 am

    Warning – following the first comment above, if you use Gmail’s spam filters you will from time to time lose good emails which Gmail whimsically considers spam. There is no way to turn of the Gmail spam filter. Thousands of folks have had important emails shoved into spam and lost job interviews, work, missed family events etc thanks to Gmail.
    you have been warned!

  4. Belask said on November 22, 2011 at 5:30 pm

    M2 is simplest, fastest and the most user-friendly email client. As far as I know, it the only email client that comes integrated with a browser. So you don’t have to run 2 applications. Emailing and browsing goes together. Nothing can beat it.

  5. Annie said on March 25, 2009 at 2:01 pm

    Had to convert to Opera for a while and have now reconverted to Thunderbird for my emails. Found a workaround for those who already have an Inbox and Sent in Thunderbird but still want to import their emails from Opera: Create in Thunderbird two (or more) new subfolders to Inbox. Export your mails from Opera according to the instructions above, and replace the newly created folders without the extension with the files from Opera. Then all you have to do is open up Thunderbird and voilá: all your Opera mails are in there too, in your Inbox subfolders. If you want to re-integrate the mails after that, it’s just Drag and Drop…

    THANK YOU fot the very helpful comments above!!

  6. MJ Oakes said on January 2, 2009 at 6:34 am

    Thanks for this–I didn’t like Opera’s handling of folders so thus the switch to Thunderbird. You’ve saved me from losing some important emails and your instructions were very clear.

  7. mmo said on January 1, 2009 at 9:29 am

    Thank you for detailed guide, the export-import was much easier than I hope it formerly!

  8. Adam said on March 12, 2008 at 4:39 pm

    Thanks so much for posting this guide. I have just successfully resurrected some very important emails from my Opera (.mbs) file into Thunderbird following your advice. All worked well and I’m a happy man!

  9. Kai said on September 28, 2006 at 11:46 am

    I found that even Thunderbird can get overwhelmed by spam, so I’m using an additional trick I found on the interweb–

    1. Set up a gmail account

    2. Forward mail from your POP account to the gmail account (if you can configure your server preferences)

    3. Have Thunderbird check your Gmail account (via POP)

    This way you can use Gmails very good spam filtering on top of Thunderbird. The result is nearly air tight.

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