Textmarker addon

Take a look to EditEmailSubject MX: it enables the user to edit the mail subject. Optionally the addon copies the original mail to a special folder.

But anyway, email has very little evidence, since it is very easy to tamper the text in th’s files.

It would be nice, if Textmarker would also be able to mark received messages.

von C-E (Entwickler) am Jan. 25, 2026 · Permanentlink

This would mean that the original message is changed, which would render the email inadmissible as evidence – it could even be considered falsification.

Let us put the legal aspects aside.
The current Webextension API’s (i.e. the interface provided by Thunderbird to develop Add-ons) does not provide a possibility to edit the e-mail content. (See messages API — WebExtension API Documentation for Thunderbird 147.0<br><br>Manifest V2 documentation)