Mail Tweak

Mail Tweak is an extension for Thunderbird 2 (with partial support for Thunderbird 1.5). It provides a variety of fixes and enhancements.

Mail Tweak's user interface is in US English, Brazilian Portuguese, Czech, French, German and Polish.

The Mail Tweak project is a subproject of Journal.

Installing Mail Tweak

To use Mail Tweak, you should normally have Thunderbird or a later release. (You can install Mail Tweak in Thunderbird 1.5, but some of the tweaks do not work in 1.5 and some of the information on this page is not accurate for 1.5.)

Install Mail Tweak in any of the normal ways that you install an extension.

Installation Example

For example, in Thunderbird choose Tools – Add-ons from the menu bar. Drag the link below and drop it in Thunderbird's Add-ons window.

Wait for the download, and allow the installation to proceed.

Restart Thunderbird.


Do not click the download link in Firefox or SeaMonkey.
Drag the link and drop it in Thunderbird's Add-ons window, or save the file to install later. In other web browsers, if the drop does not work, click the link and save the file to install later.

Current version
Here is the download link for the current version:

If you saved the file to install later, install it like this: start Thunderbird, then in Thunderbird choose Tools – Add-ons, press the Install... button, and select the file that you saved.

Note:   Mail Tweak version numbers have no relationship to Thunderbird version numbers.

Using Mail Tweak

Configure Mail Tweak by using its Options dialog.

To open the Mail Tweak Options dialog when you first install Mail Tweak, press the Options... button at the bottom of the About Mail Tweak window.

To open the Mail Tweak Options dialog at any other time, choose Tools – Add-ons. On the Extensions page, select Mail Tweak. Then press its Options button.

Note:  This screen shot shows an early version of Mail Tweak. Later versions have more tweaks.

After making a change, optionally check the box: Reload windows to apply changes now. If you check this box, then Mail Tweak will try to apply your changes immediately, and Thunderbird's main windows will be reset. Alternatively, restart Thunderbird after making changes.

Note:  Reloading the Compose window does not always work, because Thunderbird might reuse an old Compose window that has not loaded the new settings. To work around this, restart Thunderbird.


Here is a list of the tweaks in the current version of Mail Tweak. Tweaks marked with an asterisk * are enabled by default.

Account Settings cleanup *

Cleans up the list of accounts in Account Settings, so that when you open Account Settings the current account is the only one expanded.

Also adjusts the size of the Account Settings window and the accounts pane.

Address lines

When you write a message, this allows you to move the splitter at the top of the message body upwards to reduce the number of address lines, so you have more room for the message body.

Also sets the initial number of address lines to the value here.

Background color inheritance

When you reply to or forward a message that is displayed in the message pane or in its own window, your new message inherits the background color of the original.

Bcc by default

Makes Bcc (instead of To) the default for addresses in a new message.

Column heading lock

Locks column headings so that the view sorting does not change if you click a heading accidentally.

When you really want to change the view sorting, hold down the Shift key while you click a column heading.

Compact from folder properties *

In the Folder Properties dialog, adds a Compact button and shows the unused space in the folder file as a percentage of its size on disk.

In a folder's context menu, disables the Compact choice when the folder is already compact.

Configuration menu *

Adds Tools – Configuration menu choices for direct access to directories and files used by Thunderbird.

Each menu choice opens a configuration directory or file using your operating system's default application, and displays its path in Thunderbird's status bar. The menu choices are:

Installation...Program installation directory
Profiles INI...Profile Manager data file
Current Profile...Current profile directory
Chrome CSS...CSS style rules for the user interface: userChrome.css
Content CSS...CSS style rules for message content: userContent.css


CSS selector

Identifies possible CSS selectors for elements in Thunderbird's user interface, to help in customizing Thunderbird's appearance.

In a Mail & Newsgroups window, choose CSS Selector... Then Shift+Click the element in Thunderbird's user interface that you want to identify.

For more information and examples, see: Mail Tweak CSS tweaks

Dialogs menu

Menu for more direct access to various dialogs. The dialogs are:

Connection SettingsFonts & EncodingsDownloadsPassword Managerabout:config
Offline SettingsSend OptionsJunk Mail LogCertificates
Items for Offline UseDownload ActionsUpdate HistoryRevocation Lists
SMTP ServersReturn Receipts Device Manager
Discard new message

Prevents the prompt when you close a message without saving it or sending it.

Disconnect when idle

Runs a script after Thunderbird has been idle for a number of seconds. You can use the script to disconnect, or for any other purpose.

To place Thunderbird in offline mode after running the script, check the box: Work offline

Activities that trigger the script include getting mail and sending unsent messages. Sending an individual message and working with Thunderbird's user interface do not trigger the script.

Place the script in your Thunderbird profile, or in Thunderbird's installation directory.

Extension options/preferences

Adds a page to the main Options/Preferences dialog where you can open extensions' Options dialogs.

Press Shift+PageUp or Shift+PageDown to switch pages. Press Ctrl+PageUp or Ctrl+PageDown to switch tabs on a page.

Focus empty Subject *

When you compose a message to a known recipient (for example, by using the Write button in the address book), places initial cursor focus in the Subject field.

This is a temporary fix for bug 207527.

Folder icons

Enables CSS style rules for named accounts or folders in the folders pane, allowing custom icons and other effects.

This is only an enabler. It has no effect by itself. To change the appearance of accounts or folders, you must write appropriate CSS style rules in your userChrome.css file.

For more information and examples, see: Mail Tweak CSS tweaks

Folder menus

Adds a Recent checkbox to folders' context menus, so that you can add or remove folders from your list of recently used folders.

Adds tooltips to the cycle buttons at the top of the folder pane, so you can see which views the buttons will show.

Optionally adds a Favorite menu to, or removes the Recent menu from, all Move To and Copy To menus.

Folder pane auto-hide

Automatically hides the folder pane.

To reveal the folder pane, move your mouse over the left edge of Thunderbird's main window.

Hide Local Folders

Hides the Local Folders account in the folders pane. (The account is still available in Account Settings and elsewhere.)

To display Local Folders temporarily, choose: View – Local Folders

Image defaults

Default settings for the Image Properties dialog in an HTML message, when you choose Insert Image...

This controls the defaults for the checkbox "Attach the image to the message", and for alternate text.

Insert menu

Adds an Insert Text file... menu choice so that you can import text from a file.

Also enables the Insert menu in the plain text editor, where the Characters and Symbols choice also works.

Keep a copy prompt

Asks you whether you want to keep a copy when you send a message. Choose Yes (default) to send the message and keep a copy, or No to send the message without keeping a copy, or Cancel to cancel sending. This allows you to send some messages without keeping a copy.

Also adds a menu choice: Options – Keep a Copy, which is checked by default when the current identity (From address) is set to keep copies of messages you send. Uncheck this menu choice to send the message without keeping a copy.

If you use this menu choice, or the Options – Send a Copy To menu choice, then there is no prompt when you send the message.

Mesage number

Adds a Message Number... choice to local mail folder context menus, so that you can select a message by its sequential number in the folder file.

This is intended to help you find a message reported as malicious by a "security" program. Note that a message stored in a Thunderbird folder cannot ever cause harm, as long as it remains in the folder. Even if you open the message in Thunderbird, it cannot cause harm. A malicious message can only cause harm if you yourself open its attached file.

A folder file may contain deleted messages, which you cannot see in Thunderbird. To remove these messages, compact the folder.

Open folder

This tweak makes various changes to help you to work with many accounts or folders in separate windows.

In the folder pane, makes the Open action in an account's or folder's context menu collapse the rest of the new window's folder pane.

Makes double-click on an account or folder perform the Open action.

Displays internal URIs in the Account Settings and Folder Properties dialogs, so that you can copy them and paste them in command lines.

Note:  To open a folder in a new window from a command line, use the switch -mail followed by the internal URI of the account or folder. You can use this, for example, to make a desktop icon that opens a particular account. For example:

thunderbird -mail mailbox://nobody@Local%20Folders/Inbox
Permanent pen

A permanent color and style for adding comments in replies.

Press the specified key or choose Format – Permanent Pen to enable or disable the pen. Look for an indicator in the formatting toolbar to show that the pen is enabled. The indicator is a colored line beside the existing color controls.

In Mail Tweak Options, specify the key, font face, size, color and style for your permanent pen.


Personalize messages

Sends each recipient an individual message, using data from your address book or a CSV file.

To use this feature, write a message by choosing: Message – Personalize...   You can address it to a list, or to individuals in your address book. Alternatively, select cards in your address book, then get a context menu (for example, by right-clicking a card) and choose: Personalize   To use addresses from a CSV file, do not specify any addresses in the message.

To send the message, press the Personalize button or choose: File – Personalize   If the message has no recipients, then MailTweak prompts you to choose a CSV file that specifies the recipients.

MailTweak creates an individual copy of the message for each recipient. The messages are placed in your Unsent folder, so if you wish you can review them before sending them.

To include data from your address book or CSV file, specify fields in your message. For example, if you specify %%firstName%% then the actual message sent will have the recipient's first name in that position in the message.

The available address book field names are the properties listed here: nsIAbCard   Field names in a CSV file are as specified in the first line of the file, but with spaces changed to underscores. For example, if the CSV file specifies the field name First Name, then type %%First_Name%% (with an underscore) in the message.

You can specify a different field marker (default: %%).

By default each personalized message has a unique internal message ID. You can turn this off to send messages with the same internal message ID (but some mail systems might not be able to handle distinct messages that have the same ID).

In each record of a CSV file, the first field that contains an @ sign is taken to be the e-mail address. Alternatively, set the preference to the name of the field that contains the e-mail address, changing spaces in the name to underscores.

CSV files are taken to be in the platform charset by default. Alternatively, set the preference extension.mailtweak.personal.csv.charset to specify the charset of the CSV file.

Note:  In Templates and Drafts folders, the default action is Edit Message As New. To personalize a template or draft, choose: Message – Personalize As New...  

Restrictions:  The following restrictions apply in the current version. Future versions might have fewer restrictions:

Preferences cache

Backs up preference settings, including account settings, and restores them automatically if your accounts ever disappear.

This tweak is only a convenience. It is not a substitute for regular backups of all your data.

Search windows

Allows multiple Search Messages windows and Advanced Address Book Search windows to be open at the same time.

Send with no subject

Prevents the prompt when you send a message with an empty subject, and sets the subject to some specified text (which can be empty).

Splitter highlight *

Highlights the splitter between panes in a window when one of the panes is collapsed and the mouse pointer moves over the splitter, making it easier to find the splitter and drag it to open the collapsed pane.

Status icons *

Adds icons in the status bar of the message window, showing the status of the message at the time you opened it.

The icons depend on the theme you are using. In the default theme they are:

Replied to
Replied to and forwarded

Note:  The icons might not be available in some themes—for example, themes based on earlier releases of Thunderbird.

Status message cache *

Displays each status message in the main window for a fixed time so you have time to read it.

Also keeps recent status messages. To review them, click on the status bar.

Tag numbering *

Numbers all your tags, not just 1 to 9.

To tag one or more selected messages, type a tag number.

In Mail Tweak Options, specify the delay to apply before a tag number takes effect, depending on how fast you type. For example, if you type 19 too slowly, then your messages will be tagged with tag 1 and tag 9 instead of tag 19.

Tag tools

Changes the interface for managing tags. Choose: Tools – Options... – Display – Tags   in the usual way.

To change the rank of tags, move them up or down the list. A message's highest-ranked tag is the tag used to set the message's color.

To share tags between profiles, either export and import them whenever you need to, or specify a pool. The pool is a file that Thunderbird reads from when it starts up, and writes to whenever you change the tag list.

Tree font

Sets the font size in the folder pane, thread pane and address book.

Themes and other customizations can override this setting.

Word count *

Counts words and characters when you are composing a message. To see the counts, select some text and look for the message in the status bar at the bottom of the Compose window.

To count all the words and characters in the message, select all the text—for example by pressing: Ctrl+A

To see the count while you type the message, choose: View – Word count

The counts are approximate, because of the way the text in a message is encoded by the editor. Also, a message is encoded differently for transmission, so the character count does not tell you the size the message will be when you send it.

* Tweaks marked with an asterisk are enabled by default.

Uninstalling Mail Tweak

To uninstall Mail Tweak, return to the Add-ons window. Select Mail Tweak and press the Uninstall button. Close and restart Thunderbird.

When you uninstall Mail Tweak, you lose your Mail Tweak options settings. If you reinstall Mail Tweak later, then your Mail Tweak options are reset to their defaults.


0.15 Translations
Background color inheritance
Splitter highlight
Tag tools
0.14 Not released
0.13 Open folder
Preferences cache
0.12 CSS selector
Message number
Search windows
0.11 Folder menus
0.10 Configuration menu—Linux fix
Disconnect when idle
Personalize—menu choice: Message – Personalize As New...
0.9 Compact from folder properties
Focus empty Subject
Personalize—menu choice: Message – Personalize...
Word count—menu choice: View – Word count
0.8 Bcc by default
Configuration menu
Dialogs menu
Personalize—unique message IDs
0.7 Not released
0.6 Folder icons
Hide Local Folders
0.5 Address lines
No subject
Discard without saving
0.4 Account Settings cleanup
Extension options/preferences
Image defaults
Insert menu
Keep a copy prompt
Personalize (experimental)
0.3 Character count with word count
Installable in Thunderbird 1.5
0.2 Status icons
0.1 First released prototype


For questions or comments about Mail Tweak, please use this thread in the mozillaZine Extension/Theme Releases forum: Mail Tweak (for Thunderbird)