Not from within the program, as far as I know. You could save the email as .eml format, which is plain text and edit that with a text editor, then import it back into Thunderbird.

There are two add-ons, Header Tools Improved and Header Tools Lite.

Editing the header is nice but I wanted to edit the body of the message. It looks like that's not an option in TB right now.

Hello there

If there is no build in option for of editing the received message. You can go for the alternative option to create a new message that copies the content by right clicking the email and select editing as new message to start a composition with the previous content , or use reply or forward functions to build upon the existing message.

Greetings googlethunderbird.

Thank you Googlethunderbird, I've done that (creating a new message) but the result wasn't what I was looking for.

It was easy to do in Outlook. I'd receive a message with all sorts of meme joke images that had been around a while according to all the indents from previous forwarding and could just edit them out to clean them up. (and save them for future forwarding)

Editing the header is nice but I wanted to edit the body of the message. It looks like that's not an option in TB right now.

Both of those add-ons allow editing of the entire message. It's stated in the descriptions.

Hello there

I think that the recommended add ons both from Sfhowes are oké. Good to hear that you found good things at Outlook.

Okay.

https://services.addons.thunderbird.net/en-US/thunderbird/addon/header-tools-improved/?src=ss

And

https://services.addons.thunderbird.net/en-US/thunderbird/addon/header-tools-lite/?src=ss

Try to use these add ons if you can. And maybe this add ons will solve the questions you were looking for, if not send a message back.

I've added both extensions to TB but using them isn't as intuitive as I'd hoped and the little bit of instructions with them isn't much help either.

It looks like creating a new message from the one I received is the what I'll have to do now that I've switched to TB.

I was hoping I was missing something with my searches for an extension to allow me to edit the incoming message as I was able to do in Outlook.

I want to thank everyone for their help and suggestions.

I'm not going to mark this query as solved at this time.

TB 142.0/Win11 message context menu has 'Edit As New Message' for me.

If that's all that's available in TB, I'll have to learn to use it but I'd still rather be able to edit the original message.

Thanks!