View and Edit HTML code in Thunderbird easily with ThunderHTMLedit addon
If you are after exactness, its impossible to avoid HTML editing or just tweaking in your email. There was for Thunderbird an addon that would let you view the source of your email and edit it. This addon won’t work in recent Thunderbird versions (after 60), and I’m glad that it won’t because now I’ve found this one that is even better.
The new addon for Thunderbird, you can download from this page (save it anywhere and from inside Thunderbird Addons section choose the “install from file” option) adds a new tab in Thunderbird’s email composer.
When you compose a message, just click the HTML tab and you will see the HTML code. Edit as you need and return to normal view.
This addon is fast and is very convenient, using all the space of the message composer and avoiding the code that represents actual images, all these miles or useless code you had to bypass in order to add a style to an image, etc. If you used before the other plugin, you know what I mean; in any case you can get this addon and enjoy composing and tweaking the HTML code of your email messages!