Current Status
This add-on does not work anymore since Thunderbird 68 or so...
See comments and user ratings here: https://addons.thunderbird.net/de/thunderbird/addon/flexible-identity/
- 2020-11-21: Now I can at least install the plugin again. Languages are not correct at all. Changes in API are a big TODO.
- 2020-11-20: I intend to upgrade this plugin to work with current Thunderbird. Because this plugin is much better than e.g. Identity Chooser ;) I hope I can give it a try this weekend.
Flexible Identity
Sometimes it's important not to mix work and personal correspondence. Especially when Thunderbird is configured to use multiple email accounts simultaneously. Unfortunately, sometimes you recollect that would be worth to check what passes to the "from", after sending the letter. It's frustrating.
It would be nice to decide who I am writing using which identity. This add-on checks the list of recipients before sending a message and displays a warning if the outbound email address or domain does not match your needs. In addition, it is possible to correct the mistake automatically (if it is allowed).
Let the correspondence will be calm and pleasant ! :)
Build and install
make package
This is classic Mozilla add-on. Just pack source as zip archive and rename extension to xpi. Documentation available on Mozilla Developer Network, you can start reading from here: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Your_first_WebExtension