The complicated part is that Microsoft Outlook and Mozilla’s Thunderbird use different email box formats. But you can do an intermediate move that will take care of the email translation between the two programs and make it easier to get all your email in Thunderbird on your iMac. That involves installing Thunderbird on your Windows PC and importing all your email from Outlook. Once your email is in Thunderbird’s format, then it can be moved to your iMac and imported into Thunderbird on your iMac.
First, start up Outlook on your Windows PC and delete what email you don’t need, and then empty the trash. (If the email is in the deleted folder but not actually deleted, it will still be moved to your iMac.) Then quit Outlook, because if Outlook is running while you’re transferring email to Thunderbird (or after), you might end up with email in the two different programs.
If you have lots of contacts in Outlook and want them moved to Thunderbird, too, they need to be moved separately in order to get all of the information them moved over completely. To do that, start up Outlook and go to the File menu, and select Export and then Address Book. Select “Text File (Comma Separated Values)” and click “Export.” Call it “exportedcontacts” or something you’ll remember and browse tot he desktop and save it there. Select all the fields you want to export and click “Finish.”
Then download Thunderbird and install it on your Windows PC. (You’ll need to be in an administer account to install software). When Thunderbird asks what kind of installation you want – Standard or Custom – select Standard, and also check the box that asks if you want to use Thunderbird as your default email program.
When it’s done installing, tick the box that says “Launch Mozilla Thunderbird Now.” The next box will ask you to import “Settings and Mail Folders,” so select Outlook or Outlook Express. Depending on how much email you have, it might take a few minutes. If Thunderbird doesn’t ask to import email, the go to Thunderbird >> Tools >> Import and select “Mail”. Select Outlook, and all your Outlook mail will be imported.
Once the import into Thunderbird is done and you see your email, you can quit Thunderbird and get ready to move your new Thunderbird email boxes to the iMac. From this point forward, don’t startup Outlook or Thunderbird on Windows, or you could end up with new email on your PC and not on your iMac.
You need to find your mailboxes in Windows, so if you installed as an administrator, look in C:\Documents and Settings\Administrator\Application Data\Thunderbird\Profiles\ and you’ll find a folder with a randomly generated string of letters. That’s your Thunderbird email profile folder.
Now, using a flash drive that is formatted for Windows (you can’t use a flash drive formatted for OS X unless you have MacDrive or some other software installed under Windows), copy that folder to the flash drive and then to the desktop of your iMac. If you exported your contacts, too, copy that export.csv file to the flash drive.
On your iMac, go to and download Thunderbird. The disk image will open and you can then drag Thunderbird to your Applications folder. Start it up and it will ask to “Import Settings and Mail Folders.” Select “Don’t Import Anything.” Next, you’ll see a box to set up a new email account setup. Cancel out of that. Then Thunderbird will ask if you want to use it as a default email client. Tick “Email” (and RSS feeds and Newsgroups if you want to).
Thunderbird now has installed itself. Now, the next step is kind of tricky. Thunderbird has set up for itself a profile, just like the profile that it did on Windows. What you do now is move just a few things from your Windows profile on your desktop into the Thunderbird profile on your iMac, and after you do that, Thunderbird on your iMac will have all your email and settings in it.
First, quit Thunderbird. Then find the Thunderbird folder on your iMac in your Hard drive under /Users/yourusername/Library/Thunderbird/Profiles/ The default profile will be named with a string of numbers and letters and “.default” like your old Windows profile on your desktop.
Open the Windows profile on your desktop and copy just the Mail folder and the single file called “pref.js” to your Thunderbird profile folder. OS X will say older files and folders already exist, and ask to confirm the copy.
Then start Thunderbird. It will take some time to index all your email, but when it’s done, all your email will be there. Test it out by sending an email or two. Keep the Windows Thunderbird profile folder on your desktop as a backup for a while, until you’re sure all your email was moved. Then you can delete it.
If you exported contacts from Outlook, go to the Tools menu, select Import, tick “Address Books” and then click next. Tick “Text File (LDIF, .tab, .csv, .txt)” and then Next. Browse and find the export.csv file on your desktop you moved from the flash drive. Select it and click “OK.” Select the fields you want to import and click “OK.”
That should do it for moving both your email and contacts into Thunderbird.