I am puzzled. Can't you just press the DEL key?

Sure, I can use the 'Delete' key, but I would like a toolbar button as well. I also cannot put a Reply toolbar button on the 'read' window toolbar. Yes, I can use a keyboard shortcut for that too, but would like a button like the legacy versions. Thanks for your comment anyway David.

Ok, I'm still puzzled. The default toolbar on the read window has buttons for reply, forward, archive, delete and more. And, you can put a Delete button on the unified tool bar as well. See attached screenshot.

Thanks David. The Delete button is present in the Message List window, but when I open a message to read it, that window has a different toolbar, and the delete button icon is not available in the Customize icons.. even if I remove it from the message list.

Puzzling. I am on latest version and I have the delete key showing. You might try revisiting the customize option. I have no suggestions

I am running "Thunderbird, Portable Edition portable apps - 1.0 - 1.0 128.4.0 esr (64-bit)". I wonder if this addition the cause?

No, I also have a portable version and it is working. There seems to be a glitch in your setup, and I have no suggestions to change it.

I really wonder if this discussion is simple at crossed purposes. This image shows Thunderbird as designed without a delete on the toolbar. David is pointing out that there is no purpose for a delete button in the toolbar as there is one in the message pane.

Somehow the original image does not show the buttons in the message header Reply Forward or delete.

Fundamentally Thunderbird's use of toolbars has changed with recent versions there is no longer a single set of toolbar items that are present regardless of context. As you suggest each context has it's own set of applicable icons for the unified toolbar . In the case of the message reading tab or window there is no delete as there is a compulsory button in the message header toolbar.

If you do not have a toolbar in the header of the message you are reading, then the issue is where is it. Not as you originally asked where is the delete for the main toolbar. As you appear to be using a heavily customized user interface, perhaps something in the customization have removed the toolbar.

Thanks Matt, just prior to reading your comment, I discovered that the "Header' Toolbar was hidden in the 'read message' window. So that resolves the 'delete button' issue to an extent I can live with . It would nice to have all the customization toolbar icons available in any window. I wish the old 'account colors' extension was comparable with the newer versions of T-Bird. The old 'Dorando key config' (custom shortcuts) was nice too, but I found a work-around with the "tbkeys-lite" keyboard duplicate message, whereas the old was instantaneous. As well, the old Edit Email Subject 2.1.1 was much more efficient than EditEmailSubject MX which takes a long time.. compared to the old which was instantaneous. Thanks again Matt

But how did you hide the toolbar in the message header. The only add-on I have even seen do it is the compactheader add-on to version 60 and it's replacement Compact Headers

One of the things that came with the adoption of mailExtensions in place of the older addons is that essentially everything is one step removed from the source. The old style addons has implicit access to everything on your computer and every part of Thunderbird. It was convenient and fast, but it was also a security nightmare. Essentially installing an addon came with having implicit trust in the addon author to do not wrong by you. In terms of Thunderbird and mail that was essentially faith well placed. Not so much for browsers.

As Thunderbird is built on "the Mozilla platform" it shares much of it's code with Firefox and the addons ecosystem is one of those shared components. There are differences, like Thunderbird calls web extensions mail extensions. The differences are really about the fact most web extension APIs are about useless for mail manipulation so Thunderbird had to build an extensive additional API's for mail in addition to the web API's Firefox builds so chose to use another name in the hopes of reducing confusion with addon developers.

I should probably also mention BetterBird. It is a soft fork of Thunderbird with many of the complaints older Thunderbird users have with the current implementation fixed or the rough edges rubbed off. It is 100% compatible with Thunderbird. I use it as well as Thunderbird and financially support the project because having competing implementations is probably good for Thunderbird's core stability. Something I have increasing concerns about.