This article gives step by step instructions for how to import folders from another profile for a new user who has never installed an extension. It assumes you're using Windows but you should still be able to follow the instructions using a file manager on another operating system. The ImportExportTools extension can also be used to export folders.
Your folders are stored as mbox files in a profile. These are text files with the folders name and no file extension. For example your inbox folder is the "inbox." file and the Sent folder is the "Sent." file. You can safely read one using a text editor to verify it contains mail messages though its not user friendly because it contains the raw message source, including all of the headers and big blocks of characters all run together whenever you have a binary attachment.
If the folder was in Local Folders or you used a global inbox it will be somewhere in the Mail\Local Folders directory within the profile. Otherwise look for a subdirectory named after the accounts mail server. For example, if you're using a Gmail POP account your inbox folder would normally be the "inbox." mbox file at Mail\pop.gmail.com. If you have multiple accounts with the same email provider the subdirectory might have a numeric suffix, for example Mail\pop.gmail-2.com.
Your folders are stored as mbox files in a profile. These are text files with the folders name and no file extension. For example your inbox folder is the "inbox." file. DO NOT try to import "inbox.msf" or "inbox.sbd" - the messages are in "inbox.". That naming convention causes a lot of confusion, it would have been a lot easier if the mbox files had a .mbx or .mbox file extension like some other email clients use.
Tools -> ImportExportTools -> Import Messages and "Import all messages from a directory" import .eml files. That is mainly used to import messages from other email clients that don't support mbox files such as Windows Live Mail. Thunderbird does support configuring an account to use maildir rather than mbox to store messages. Thunderbird's implementation of maildir stores all of the messages as individual files using the .eml format. Each file has a filename that is a string of digits and has no filename. Because they don't have a .eml file extension you need to choose "All files" in the file picker.
You could export your mail folders instead as mbox files using using Tools -> ImportExportTools -> Export folder, as *.eml files using Tools -> ImportExportTools -> Export all messages in the folder -> EML format (you could import them later on using Tools -> ImportExportTools -> Import All Messages from a directory -> also from its subdirectories), or in several different formats that are only meant to display the contents (can't import them).
If your old email client is still installed, the easiest solution is to import the e-mail, address books and settings using Tools -> Import. If it is not installed or Thunderbird doesn't know how to import data from it, typically you need to find some way to export or convert your old email client's mail files to either .EML or mbox files, and some way to export or convert the address books to .CSV or .LDIF files. And if you just need to transfer email between email clients, another option is doing so indirectly via a mail server.
Thunderbird, Netscape, Mozilla Suite and SeaMonkey use mbox files to store the messages for a folder. The ImportExportTools extension can import and export mbox and .EML files. Many email clients use mbox files (regardless of whether they use no file extension, .mbx or .mbox as the file extension) to store messages or provide a way to export folders as mbox or .EML files due to the popularity of Eudora and Outlook Express. Sometimes email clients use "Unix format" to refer to a mbox file since the format was originally developed for Unix systems.
If you have problems importing .EML files using the ImportExportTools extension try using eml2mbx to convert the .EML files to a mbox file and then import the mbox file using the ImportExportTools extension. A Google search will find several eml to mbox conversion programs. Whats unusual about this one is that provides a lot of control over how it converts the .EML files using a "eml2mbx.ini" file.
Open Entourage and drag and drop the folders to the desktop. That will create mbox files with an .mbox file extension. Either drag and drop them to the appropriate directory in your Thunderbird profile or import them using the ImportExportTools extension.
How To Migrate From Evolution To Thunderbird In Ubuntu Intrepid describes how to migrate the mail, calender, tasks and address book. It was written when Evolution defaulted to using mbox files, just like Thunderbird does. Evolution 3.2.0 and later uses maildir files. If you created your Evolution profile using a version that defaulted to maildir you will need to use a tool to convert maildir files into mbox files for multiple folders, such as maildirarc or maildir2mbox. Then you can import the mbox files using the ImportExportTools add-on, and resume using the article for how to import your other data.
Groupwise supports SOAP, POP and IMAP accounts. The easiest way to migrate mail would be to drag and drop folders from a Groupwise IMAP account in Thunderbird to another IMAP account (such as Gmail) in Thunderbird. If thats not possible GWSave does a bulk export of messages to .eml files. You could use the ImportExportTools add-on to import them into Thunderbird.
See Mail Utilities for some utilities that can be used to import messages if you no longer have the Microsoft email client installed. For example, you can use MailStore Home to export a .pst file as .eml files and then use the ImportExportTools add-on to import them into Thunderbird. There is also a trial version of a mbox to .pst file converter from Kernel Data Recovery that can save the mail in an existing .pst file or create a new one. Pegasus
Windows mail stores the messages as .EML files. They are normally stored within the C:\AppData\Local\Microsoft\Windows Mail directory. If you can't find them look in the Tools -> Options -> Advanced -> Maintenance -> Store Folder to find where Windows Mail stored them. The best way to import .EML files is with the ImportExportTools add-on, it lets you import all of the .EML files in a directory in one step using "Tools -> ImportExportTools -> Import all eml files from a directory". However, if you only have a few .EML files you could drag and drop them from Windows Explorer to a folder in Thunderbird instead.
Export the contacts using the Windows Contacts program as a .csv file. You can import it using Tools -> Import -> Address books -> Text Files. See this article for more information about how to export the contacts.
Export the messages as .EML files using the ImportExportTools extension. Then use File -> Import -> Messages in Windows Live Mail to import all of them. If it doesn't like the layout of the directory tree you can always launch Windows Live Mail, open a folder, and drag and drop the .EML files you want to import, to that folder. Outlook Express and Windows Mail support importing messages by dragging and dropping .EML files too.
Google webMail Filer for Thunderbird is a utility to upload messages from Thunderbird's mail folders to your Gmail account. It deals with issues such as not uploading duplicates, Unicode, Gmail nested labels and the Google mail quota that its not clear that GML knows about. Its only available for Windows (its a .NET program that won't run under Wine or using Mono). Its a better way to upload mail to Gmail but since it is Thunderbird specific program that only knows about mbox files its not useful if you are trying to migrate messages from another email client. Version 126.96.36.199 (released 2013-01-29) is the last version available. The author appears to have stopped all work on the software. Ghacks has an article about the utility here.
There are four main versions of the mbox format. Thunderbird, Mozilla Suite, Netscape, Portable Thunderbird, Postbox, Spicebird, SeaMonkey and the open source version of Eudora use a slightly modified version of the mboxrd variant of this format. The proprietary version of Eudora uses a slightly modified version of the mboxo variant. Most Windows email clients that use mbox files will use a mboxo or mboxrd version, and you should have little trouble importing them. Under Linux you're more likely to run into an mboxcl or mboxcl2 version, which is incompatible. Both Kmail and Evolution use a compatible version. You might try migrating your messages to Kmail as an intermediate step since it supports importing numerous formats.
Unless you are an advanced user its generally preferable to use an application to import or export a folder since that typically sanitizes the file to minimize any incompatibilities. If you use IMAP's optional offline mode to create a local copy of remote folders, think ahead about how you will deal with any potential synchronization issues. To manually import/export mbox formatted files:
Another solution would be to sign up for a free IMAP account (such as Gmail), add the account to both Outlook and Thunderbird, and then use the IMAP account as a intermediary to transfer your mail (without importing or forwarding it). You would do this by copying or moving the messages to the folders in the IMAP account. Both email clients would be able to use those messages. Think of it as sort of like a file share, except it is for messages. This works because IMAP supports remote folders (on the mail server) that you can access just like they're local folders. See Migrating messages using a mail server for more information.
Normally you import by setting Outlook as the default email client, and then use Tools -> Import -> Mail within Thunderbird. This method uses SimpleMAPI calls to Outlook, and Outlook accesses the contents of the personal folders (.pst) file. See Import_from_Outlook_Express for information on how to import from more than one identity. If some of the messages aren't imported correctly, a common workaround is to import the messages into Outlook Express, and then import the messages from Outlook Express into Thunderbird. If you're switching to a new PC where you're going to run Thunderbird (instead of Outlook) its recommended that you import your messages into Thunderbird before getting rid of (or cannibalizing) your old PC. 2b1af7f3a8