Thunderbird can import your messages and OS X address book, but it cannot import your account settings. (Currently, message and address book import is only functional with Apple Mail 5.0 or earlier.)
Your imported messages will appear in the Local Folders account, in a folder called "Apple Mail Import".
Thunderbird will read your OS X address book and display it in the Thunderbird address book window! From the menu bar, open the Window menu and click on Address Book. Your OS X address book will appear in the left pane.
If you want to import it to the Thunderbird address book, just drag and drop entries from the Mac OS X address book folder to the Personal Address Book.
Windows Mail is the default mail client included with Windows Vista. Windows Live Mail is the email client bundled with Windows Live Essentials. Both client programs store emails in the .eml file format. In order to export messages from Windows Mail or Windows Live Mail to Thunderbird, you must export messages from the Windows application and import them into Thunderbird. A similar method is needed to export contacts from Windows Mail or Windows Live Mail to Thunderbird.
To find the location of the email files in Windows Mail or Windows Live Mail, go to Tools > Options > Advanced > Maintenance > Store Folder.
Importing Windows Mail (.eml files) into Thunderbird is enabled by the third-party add-on ImportExport Tools. Download and install this add-on to transfer messages from Windows Live Mail to Thunderbird.
In order to import Windows contacts into Thunderbird, you must export the contacts to a text file (.csv format) and import the file into Thunderbird. See the Export contacts from Outlook article at Microsoft.com for instructions on how to export contacts in Windows.
After creating the required file, you can import your contacts using the import wizard:
In the Import Address Book window that appears, use the Move Up and Move Down buttons to match the address book fields on the left to the correct data for import on the right, and uncheck items you do not want to import. When you are done, click OK. Your contacts should now be imported and ready for use in Thunderbird.
Note that if you are having problems importing the fields properly (like when all record data to import shows up inside the first field row when inside the Import Address Book window), this is probably a result of an exported .csv file containing semicolons instead of commas, or the other way around. This usually happens because the separator in Windows Regional settings does not match the one for the Thunderbird locale, for instance when you exported a .csv file using an English Windows version and try to import it into a non-English version of Thunderbird. In this case, you should make the list separator match in your Regional settings before exporting the .csv file, or you could edit the already exported .csv file using a text editor and replace all semicolons by commas (or vice versa), and retry the import step.
The normal Thunderbird import process requires that you have Eudora or Outlook installed on your computer. If you do not have them installed, there are alternatives as noted below.
To use Thunderbird's import wizard, you must use an older version of Thunderbird, because the wizard is disabled for Outlook and Eudora in Thunderbird version 38 and newer versions. Install version 31.8, import your data, then upgrade to the latest version of Thunderbird via the built-in update mechanism.
An alternative to Thunderbird's import wizard is to find a tool to transform your data to mbox format (.mbx), and then use Import Export Tools add-on in Thunderbird to import the mbox files. One such mbox conversion tool for Eudora is Eudora Rescue.
If Eudora is not installed and you want to use the Thunderbird import wizard, you can easily change the Windows registry to point to your Eudora files, then run the import wizard.
=== Registry file, adjust file location as required === Windows Registry Editor Version 5.00
dLine] "Current"="Anything H:\\SCRATCH\\Eudoradata Anything" ===
The following instructions describe how to import messages and contacts from Evolution.
Thunderbird and Evolution use the same file format (called mbox) to store your mails, so its not difficult to import them manually.
If you are using a web-based application provided by your Internet Service Provider (ISP) to access your email, you probably only need to configure your account information to switch to Thunderbird. See Manual Account Configuration for instructions. Also, see ISP Configuration Settings for instructions on specific ISPs.
Once you have configured your account in Thunderbird, you should be able to access all your messages (both incoming and sent). However, your address book (contacts), mail filters and other settings will not be automatically transferred to Thunderbird.
Some web-base email applications allow you to export contacts in text or comma-separated formats. Check your ISP's documentation for more information. To import contacts into Thunderbird, select Tools > Import… and follow the instructions on the screen.