From the bug report , which also has a screen shot mock up "This would make it easier to identify the folders of diffrent mail accounts. This would also make sense for the top account nodes."
I'm not sure this can be done, once the message and been received.But it is possible to do before sending. There are two addons https://services.addons.thunderbird.net/En-us/thunderbird/addon/inline-image-resizer/ https://services.addons.thunderbird...
