Thunderbird Extension Custom Sender Address and Reply


The Thunderbird extension Custom Sender Address and Reply (Cusedar for short) is a merge of
Flexible Identity
Reply as Original Recipient
with new features added.

Cusedar allows the user to define custom “From”-addresses based on the recipient mail address. Either by defining rules in the extension options, or in the address book.
In addition, when replying to a mail the extension can check the “To”-address of the received mail and with a regular expression match this address is used as the new “From”-address. Thus ensuring you always reply with the correct identiy.



Installation methods

There are various installation methods available, depending on your needs and preferences.
They are sorted in the following by their likelyhood, i.e. when you’re unsure select the first one you feel comfortable with.

Please be aware that Cusedar and Flexible Identity will compete about the same controls, because they are akin.
So expect trouble when you have both extensions installed, which is strongly discouraged.

Install from Thunderbird Add-On Site

Find it here:

Download prepared package

Head over to the release page:

And fetch the provided xpi.bin file.
After you renamed it to .xpi (otherwise Firefox blocks the download) you can install it manually in Thunderbird (Add-On Manager, Install Add-On from file).

Create own package

  1. Download or clone this extension
  2. Change into the directory
  3. (Optional when you made local changes)
    git clean -i -x
  4. zip -r -9 ../cusedar-VERSIONNUMBER-tb.xpi . --exclude .git/\*

Local installation

For a local installation create a file named
with it’s only content being the path where you downloaded or cloned this extension.

This is the perfect starting point for your own modifications.

Update from Flexible Identity

  1. Close Thunderbird, when it’s currently running
  2. Open file prefs.js in your Thunderbird profile (make a backup),
    replace text “extensions.fid.” with “extensions.cusedar.”
  3. Rename file “flexible-dentity.json” to “extension-cusedar.json” in your Thunderbird profile
  4. Start Thunderbird
  5. Uninstall Flexible Identity
  6. Install Cusedar

License and Origin

The original source code files are licensed under different licenses

All changes afterwards are dual-licensed under both GNU General Public License version 3.0 and Mozilla Public License version 2.0 .


If you have any questions, just write me or create an issue (see below).