Turn the Contact Pane on and use that. Open a Write window and press F9 to toggle it on. Select the Contact or contacts for the message. Hold the control key while clicking to select multiple contacts. Then use one of the Add To buttons to address the message.

There are many ways to populate the addressing box and you seem to have stalled on only one of them. What is a "list" in your world? Where do these "lists" you want to drag-and-drop come from?

Drag-and-drop is probably the least-used method. Have you discovered the Contacts Sidebar yet? I suspect not because I think you might not be asking this question if you had. In the write window, hit F9 to toggle it on and off.

Anyway, set the address box to Bcc: before doing your drag-and-drop. Or use "Add to Bcc:" in the Contacts Sidebar. Or make your selection and use right-click and "Add to Bcc:"

If you use Bcc: often (bravo!) then the Use Bcc Instead add-on may be of interest to you. It will propose using Bcc: (and will apply the change for you) when you reach some threshold number of addresses, and it adds a feature for changing between To:/Cc:/Bcc: en bloc.

Another approach is an add-on which permanently sets three boxes to To:, Cc: and Bcc: and allows you to add addresses serially, as is done in Outlook. It has certain limitations which, for me, rule it out. I can't recall its name right now.

thx. I've had lists for years. Always used Pegasus Mail because it was easy to figure out. Didn't have to hunt for keys or add ons. But now that guy has quit and there won't be any updates.

I tried F9 or whatever. Waiting to hear back from someone on my list to see if it worked.

I simply created a list in t-bird and pasted the emails in there. That always worked with the other one.

I see f8 gets rid of the stupid view/reader pane or whatever. Is there a list somewhere of all t-bird shortcuts?

You're throwing the word "list" around and I still ndon't know what you mean by it. Could be an address book, or a Mailing List. Please try to be more precise.

Look at this add-on: MRC Compose

https://addons.mozilla.org/en-US/thunderbird/addon/mrc-compose/

BTW, experienced users save themselves many cumulative keystrokes by using the allegedly "stupid view/reader pane". They also are not flying blind into whatever the next email message is. I consider the message view pane to be safer than the open-in-a-window-or-tab malarkey, and certainly more efficient.