This article describes the major changes in Thunderbird version 3.

Accounts

• There is a new Mail Account Setup Wizard accessed via File | New | Mail Account. After you enter your account information, Thunderbird attempts to fetch details about how mail at that domain should be configured. (Setup and configuration information has been collected by the Thunderbird team.) Note that the domain name portion of the email address is the only information sent to Mozilla Messaging's servers and that Thunderbird fully abides by the Mozilla privacy policy. If Thunderbird doesn't find configuration information, it tests for the existence of common defaults (such as "imap" and "pop" prefixes to the domain name and listeners on standard ports). If those can't be inferred from the mail account domain, you must manually configure the account.
• With new IMAP accounts, offline folders are enabled by default. When necessary, existing IMAP folders are configured to be offline. Disable either in the individual folder's properties or in Account Settings | Synchronization & Storage. (Click the Advanced button on the Synchronization & Storage page to access a folder list that allows you to specify a group of folders for offline storage.)
• Signatures can now be created on the Account Settings page (or by clicking the Manage Identities button). If you check Use HTML, you can use HTML markup tags. If you specify a signature file, the contents in the Signature text field will be ignored. GIF, JPEG, or PNG-format images can be specified as an attachment file. Signatures can be omitted when replying or forwarding; this is configured on the Composition & Addressing page of the Account Settings.
• When new POP accounts are created, by default messages on the server are deleted after 14 days. To change this setting, click on Tools | Account Settings, then select the Server Settings page beneath the account name in the left panel. Alter the values in the Server Settings section of the page according to your preferences.

Folders

• Smart Folders (renamed to "unified folders" in subsequent releases) combine mailboxes from multiple accounts. Access Smart Folders either by selecting View | Folders | Smart Folders from the menu, or by clicking the forward and back buttons (which will cycle through all folder views) located in the top right corner of the Folder pane. To revert to the standard view (of folders groups under accounts), select View | Folders | All from the menu, or use the arrow buttons in the top right corner of the Folder pane.

Message list

• When threaded email messages are collapsed, Thunderbird 3 displays a summary of all the messages in the thread when the collapsed message is selected in the Message List pane.
• When multiple messages are selected in the Message List, the message pane displays summary information for the selected messages.
• When you do an operation on collapsed threads, the operation applies to messages in the collapsed thread. E.g., if you select the top-level message in a collapsed thread and press delete, Thunderbird 3 will delete all the messages in the thread.
• When you change the columns that are displayed in the Message List the changes are stored on a per-folder basis (meaning that you can have different column configurations for different folders).

Messages

• A star symbol is displayed to the right of email addresses in the message header (such as "from", "cc", etc). If the star is outlined but not filled in, the contact is not in your address book. Click the star to add the contact to the address book. If the star is filled in, the contact is already in your address book. Click the star to edit contact details.
• When a message is received that was sent via a mailing list, the reply button now also has a reply list option (in addition to reply and reply all). (The message must have a "List-Post" header in order to trigger the display of this button.)
• The compact header view (where display of the message headers was compressed to a single line) has been removed. There is now an extension available that provides this view.
• Images embedded in messages can be resized to fit the window width. Use the arrows to toggle between "fit to width" and "original size".
• If an email address in the From, To or CC header matches one of the configured accounts, the email address will be replaced with the text "you". You can see the related email address by hovering over the text. To disable, go to the Advanced | Reading & Display preference page and uncheck Show only display name for people in my address book.

Tabbed folders and messages

The Thunderbird interface now supports multiple tabs:

• To open a message in a new tab, double-click a message in the message list (or press Enter when a message is highlighted). Alternatively, right-click a message in the message list and select Open Message in a New Tab.
• To open a folder in a new tab, right click the folder and select Open in New Tab.
• Middle-click a message or folder to open it in a tab in the background.
• To close a tab, either click the close symbol or use the Ctrl-W keyboard shortcut.
• Click the drop-down list to the right of the tab toolbar to view a list of tabs and select the tab to display.

Composition

• If a portion of a message (text and / or images) is selected when you click Reply, only the selected portion will be quoted in the reply, not the entire message.
• Forwarded messages are now sent inline rather than as attachments.
• If you hold down the Shift key when clicking the Forward button, the message will be composed in the format that is the opposite of your default (that is, HTML if your default is text and vice versa).
• Signatures must be manually enabled for forwarded messages (on the Composition & Addressing page of the Account Settings).
• There is a new preference on the Composition page for disabling or enabling the inclusion of extensions suffixes on attached file names. This can prevent situations where mail servers filter attachments because the message attachment is of a restricted file type.
• Thunderbird now checks that a message has an attachment when the word "attachment" occurs in the email. This can be disabled (or the list of keywords can be altered) in the Preferences, on the Composition | General page.
• The PNG format (as opposed to JPG) is now the default image format when pasting images into messages.
• When a character is inserted into a message that cannot be represented with the default encoding, conversion to UTF-8 is now performed automatically without prompt.

Address book

• A new birthday field has been added.
• "Cards" have been renamed "Contacts".
• You can now associate an image with a Contact.
• On Mac OS X, the system's address book is read by default.

Search

• Thunderbird includes a new message indexing and search system (Gloda) that improves search performance, provides sophisticated full-text search capabilities and faceted (categorized) search results. The new search capability is enabled by default; the search text box is located by default on the right side of the toolbar. Enter one or more search terms - you will be given the choice of whether the search should treat the terms with an "and" or an "or" operator. Alternatively, enter an email address. The search performs autocomplete on addresses and allows partial text matches (for example, "ragat" matches "operagator"). Search results are displayed in a new tab, with "facets" (categorization and additional classification options) displayed in a panel on the left. A timeline is displayed above the search results, allowing you to view match statistics and drill down chronologically on matches.
• Thunderbird is now integrated with Windows Vista, Windows 7, and Mac OS X Spotlight search capabilities. You will be prompted to enable this functionality the first time you start Thunderbird, and you can turn it off or on at any time by going to the Advanced | General page of the Preferences.

Performance, stability and interface enhancements

• Thunderbird will now download IMAP messages in the background to allow for faster message loading and better offline operation. This feature can be enabled on an individual folder basis (via folder properties), or for all folders in an account (via Account Settings | Synchronization & Storage).
• The Activity Manager (Tools | Activity Manager) records interactions between Thunderbird and the email provider, providing helpful troubleshooting information.

Miscellaneous

• MathML is now enabled by default.
• Video content can now be played in Thunderbird. To play a video embedded in an email, access controls from the right-click context menu. (The controls are not automatically enabled because JavaScript is disabled in emails for security reasons.) Video content in RSS feeds will display the controls as expected.
• Thunderbird now has an Add-ons Manager (Tools | Add-ons) that can be used to find, download, and install Thunderbird Add-ons (including Extensions, Themes, and Plugins).
• Thunderbird now has an Archive folder system which can store messages moved from the Inbox (or other folders). The location of the archive is configured on a per-account basis, on the Copies & Folders page of the Account Settings. To archive a message, click the archive button on the message header. To archive multiple messages, select the message in the Message List then select Message | Archive from the menu. By default, archived messages are stored in folders named after the year when the message was sent (not when the message was archived).
• For Mac users, Thunderbird can import messages from Mac's Mail.app and use Growl for new mail alerts.
• For Gmail users, there is better recognition and integration of Gmail's special folders (such as Sent and Trash), including non-English versions of Gmail. Thunderbird also uses All Mail as the Archives folder.
• There is now a Compact button that has the same functionality as the Compact menu item. You can customize the toolbar to access the button.