From MozillaZine Knowledge Base

Apple Mail, Outlook Express, and Outlook cannot recognize Thunderbird's mailbox files in order to import them. If you try to import the mailbox files, you may get an error message such as "Import Error—The mail folder could not be opened. If another application is using this file, please close it and try again."

Below are some ways you can export your Thunderbird e-mail into Apple Mail, Outlook and Outlook Express based on actual users' experiences. Before trying any of these methods, it is recommeded that you first try to get rid of all special characters in the names of mailbox folders (for example, "@", commas, and so forth). Otherwise, you might run into trouble later and might not get error messages even if something wrong does occur during the import process.

If and only if you have a small number of messages in your Inbox, you may also just select each message individually and click "File -> Save As -> File" so that the e-mail is now saved with an .eml extension, which you can then import into Outlook/Outlook Express or most other e-mail clients. If all else fails, you can still open the file with any text editor such as KWrite, gedit, or Notepad.

Using Netscape Communicator V4.7

You can use Netscape Communicator V4.7 to export email folders to Outlook(Express). Follow the following steps:

• download and install Netscape communicator V4.7 from Get Netscape. Do not run Netscape yet!

• Go to the "Mail" directory in your Thunderbird profile folder. (If you are using the Global Inbox in Thunderbird, you will need to go to "Local Folders" inside the "Mail" folder.)

• Get Thunderbird's mail files (the ones which have no filename extension, such as "Inbox"). Copy them to the message folder of Netscape Communicator. You can find this folder in Netscape Messenger under Edit->Preferences-> Mail & Group News -> Mail Servers. Do not copy the .msf files!

You can also use the MBOX autosave extension in Thunderbird to save your folders: Get MBOX Autosave

• Start Netscape Messenger

• Now all folders will be loaded by Netscape. In order to have them ready for export, you should open/view the folders one by one. This way, Netscape creates the index .snm files.

• Now start Outlook Express and use the import message function: File->Import Messages->Netscape Communicator and select the location again where Netscape stores it mailfolders. All messages will be imported perfectly.

• From Outlook you can now import again from Outlook Express

Using Eudora

You can try importing your Thunderbird mail into Eudora, and then importing into your other mail client from there. However some users have reported that Eudora actually will not properly import Thunderbird messages with attachments or rich text formatting. (See this page for user discussion.)

• Get Eudora (there is a freeware Light version) and install it.

• Go to the "Mail" directory in your Thunderbird profile folder. (If you are using the Global Inbox in Thunderbird, you will need to go to "Local Folders" inside the "Mail" folder.)

• Get Thunderbird's mail files (the ones which have no filename extension, such as "Inbox"). Copy them to a new location and then rename them to have an ".mbx" extension. For example, "Inbox" should become "Inbox.mbx".

• Make sure Eudora is closed. Find its profile folder (on a default install on Windows, it is at C:\Documents and Settings\myusername\Application Data\Qualcomm\Eudora) and copy the newly renamed Thunderbird mail files to that folder.

• Now open Eudora and access all the folders you just copied. This makes Eudora create the ".toc" index files that Apple Mail, Outlook Express, and Outlook look for in the import process.

• If you still experience trouble importing using Outlook, you should try importing the Eudora ".mbx" files into Outlook Express and then into Outlook.

NOTE: Because of differences between Eudora .mbox and Thunderbird's .mbox, all attachments will be lost by using this method

Using the ImportExportTools extension

The ImportExportTools extension supports exporting folders as either .eml or mbox files. While it might be laborious, it would be straight forward to export all of the messages in one folder, select all of the .eml files in Windows Explorer and drag and drop them to a POP accounts folder in a Outlook Express window, and then repeat as needed for the remaining folders. Outlook Express will import the .eml messages into the folder when you do that.

Outlook doesn't support dragging and dropping of .eml files but you could use Outlook Express as an intermediary, and then import them from Outlook Express into Outlook.

Older versions of Mail.App supported importing mbox files. See if the current version supports importing folders from a email client like Entourage that knows how to import mbox files as folders. If so, you could export the mbox files, import them in the intermediary email client, and then import them from that email client into Mail.App.

If using Windows Vista, where Outlook Express is not available, you would drag the .eml files to the Windows Mail preview pane. Outlook should then be able to import from Windows Mail.

Special software

You could also use third-party utilities such as mbox2eml, mailbag assistant, Aid4mail, IMAPSize, or mbx2eml to create .eml files and then drag and drop them into Outlook Express (plain Outlook won't work). The Thunderbird AutoSave extension can also be used to save an entire folder as individual .eml files [1].

Using the Mailredirect extension

The Mailredirect extension supports forwarding one or more messages while making all of the important headers look like the headers in the original message. However you'd lose all status flags, you'd have to organize the messages into a folder hierarchy again, you'd probably have to do it in several steps to work around limits on your mailbox size, and have to deal with limits on how many messages your email provider lets you send within a hour. See this article for more information.

Using IMAP

• Create a IMAP account within Thunderbird. You could either use an existing account on a IMAP server, install a IMAP server such as hMailServer on your PC and create one, or sign up for a free IMAP account with either Gmail or AIM . They both provide free IMAP accounts with large mailboxes.

• Duplicate your local folder structure as best you can (IMAP clients usually require every folder to be a sub folder of Inbox) in that account, and then copy the contents of each of your local folders to the corresponding folder in the IMAP account.

• Create a new IMAP account in the email client you want to switch to and configure it to use the same remote folders (i.e. configure it to use the same IMAP account on the same IMAP server).

• Duplicate your local folder structure as best you can and copy your messages into its folders.

This works because IMAP lets you copy/move messages to/from the remote folders (on the mail server) as if they were local folders. It supports a client-server view of the world, not a download-centric one such as POP.

Depending upon your IMAP server you may lose some of the status flags such as 'replied to'.

See also

• Mail utilities
• Using Outlook (Express) contacts with Thunderbird or Mozilla Mail
• Import from Outlook Express