Message Composition
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Custom Sender Address and Reply Requires Restart
Select sender mail address based on the recipient and reply with the same address
Expand mailing lists
Adds an 'expand lists' button to the compose window. It replaces all mailing lists with their contacts.
AutoCopy_rebirth Requires Restart
Lightweight add-on that automatically copies any highlighted text to clipboard.
Proton Mail Toolbar Button
Adds a Proton Mail button to the toolbar. The button simply opens a new tab with the https://mail.proton.me webpage.
Folder Account
Lets you associate user accounts and identities with specific folders. Great for multiple users who share TB, or for managing mailing lists.
Copy Message ID
Adds a button to the message view toolbar to copy the message ID to the clipboard. This is useful when sending email replies via the command line.
changeQuote
It's an extension that changes the format of reply header.
You can choose between the standard Thunderbird reply header, a detailed reply header or a Customized reply header.
You can configure it in the Tools ->Add-on Preferences -> changeQuote.
Markdown Here Revival
A revival of the popular Markdown-Here addon for Thunderbird 78 and beyond.
Markdown Here Revival is a Thunderbird extension that lets you write emails in Markdown and render them as HTML before sending.
Aify
Rewrite or generate text based on promps using OpenAI's API.
Configure on settings page (make sure to save) and start to use when writing your emails!
You must have a payment method on record with OpenAI and an API key. OpenAI charge for use.
Stationery Requires Restart
Extension to mimic Outlook Express Stationery.
Allow you to use HTML files as templates for mail. Also allow custom template in replies or forwarded mail!
BorderColors GT Requires Restart
How many time you sent an email from your wrong email address?
This add-ons allows you assign a different color to the compose window border for each of your email addresses. So you can immediately view from what account are you writing.
BorderColors D
Shows a colorful border around the "New Message" window, so you can tell different identities apart.
Builds on the original BorderColors and the "GT" version, adding different border styles.
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.
To create your own collections, you must have a Mozilla Add-ons account.