Thunderbird pastes image into things at their full size. It does not scale them up or anything. Generally folk that find the size a surprise are not aware how large their images really are.

Word routinely sizes images to fit the space. Microsoft have always catered to putting the document on paper because that is the purpose of a word processor, and you can't just stretch paper like you can HTML and images on screen. I am not aware of any plain text documents that can contain images so I really can not look at your assertion you can paste images into text documents.

Resizing an image is relatively straightforward. Use the format > Image properties menu items.

Or these couple of addons make it even less onerous. Make your photos smaller, so they don't take forever to email. https://addons.thunderbird.net/en-US/thunderbird/addon/shrunked-image-resizer/?src=search A V115 XPI of the addon can be downloaded here https://github.com/memeller/shrunked/releases

Or you could look at https://addons.thunderbird.net/en-US/thunderbird/addon/compose-responsive-images/?src=search When writing new emails, newly inserted images are made responsive by setting style="max-width:100%" and removing width/height attributes.

But this behavior changed in the last two weeks. I just copy and past the header of phishing emails to send back to Xfinity to notify them of phishing activity. Copying the header and pasting into an email to them has always previously pasted as original size in those emails. Until two weeks ago. Now, it won't fit into the email. Sumpin' changed.

Sumpin' changed.

Yes, Thunderbird uses a HTML rendering of the three pane view and email display after V115. Prior to that it used a custom deprecated Mozilla layout tool (XUL).

But seriously who is reading your images when you send them? When you are asked for headers, they are text. Sending the image probably sees the email stripped of the image before it is even delivered. Many corporate "notification" systems simple do not support image or in some cases even HTML as the header is plain text.

BTW the header is the text displayed when you display the message source (ctrl+U) before the body of the email is shown. Not the rather diagnostically useless information shown in the message display.

i checked the xfinity web site and they are asking for full text headers, not an image. https://internetsecurity.xfinity.com/help/report-abuse For spam they are asking the original email be send to them as an attachment. (message menu > forward as > attachment.)