Warns if you send mail from or to a specified domain. If there are multiple accounts in your profile, you can isolate one so that you can't send mail to that domain from outside or vis versa without warning.
Don't Send Linked Files Requires Restart
Prevents sending of linked files if they are file: URLs.
Identity Checker Requires Restart
This add-on checks to sender identity when send a message.
random(signature) Requires Restart
Updates a given signature file in regular intervals.
Rage Hoye Requires Restart
Prevents you from sending offensive mails based on a keyword list
Attachemnt Encoding Detector Requires Restart
To detect file encoding of attachments, this forces to Thunderbird to use an encoding detector for a specific locale instead of the generic one.
BccBlocker Requires Restart
A ThunderBird extension to prevent the use of the Bcc field.
Bcc is the worst thing ever.
It kills transparency inside an organization.
If you use the Bcc feature, you should ask yourself why..
PennyPost Requires Restart
This extension makes it very easy to generate and attach stamps to outgoing mail. It also automatically detects and verifies stamps on incoming emails. The MBound algorithm requires a 16MB fixed table to work, HashCash is more CPU intense.
RM: EXTERNAL: Requires Restart
Removes 'EXTERNAL: ' from the start of an email subject if it is preceded by 'RE:' or 'FWD:' (case insensitive). The removal is done after the 'Send' button is pressed.
FastCC Requires Restart
A Thunderbird extension that let you switch to cc: with the ALT+CTRL+C keyboard shortcut!
SendToSecondEmail Requires Restart
This Extension lets you send Mails to both, first and second email address...
Posting Style Enforcer Requires Restart
Automatically converts top-posted messages to use bottom-positng or vice versa. Interleaved posts are left alone. Detects automatically added text and supports a per-contact list of exceptions.
ThunderBird Ticker Requires Restart
Extension for creating support tickets based on mail.
Patch to Alert Invalid Addresses Requires Restart
Shows alert if there is any invalid address in sending message.
~okeanos for Filelink Requires Restart
Add ~okeanos support to Thunderbird's Filelink feature.
Synnefo for Filelink Requires Restart
Add Synnefo support to Thunderbird's Filelink feature.
Smart Quotes Requires Restart
Enables “Smart” Quotes for Thunderbird Email
HtmlHighlightr Requires Restart
Provides source code highlighting in editor's "Insert HTML" dialog.
nomapi Requires Restart
not a mapi plugin
Help in reminding mails to be answer or sent again. Choose a reminder date for each received or send message that are highlighted in the message list, depending on their status (expired, soon to exprire, to be reminded). Sending a reminder is eased.