Clicking view>density>compact should improve the message list pane, and the layout you selected lets you adjust the message view size. If your message list is long, you might investigate changing layout to vertical view.

Thanks for the reply. Under density, compact is selected. Under the layout, I have tried the classic and wide view options no change.

This problem didn't occur until this update. Most of my issues would be solved if I could just shrink the incoming messages box or increase the message box size. Very frustrating

Try the vertical view. That may resolve your issue.

Thanks for the reply. I don't like it, but that's what I am using. The darn message header box takes up about half the screen. There used to be a add-on called compact headers that took care of the issue, but of course, doesn't work with this version.

I still wondering about the purpose of this box anyways. Of course, I know the to, and reply to ( would be in the message) The only thing useful is the subject and of course the action buttons. It's hard to believe there isn't an option to shrink that. I have been with Thunderbird for years, but it appears to be about time to check out other email clients.

The boxes you refer to are called panes, described at https://support.mozilla.org/en-US/kb/getting-started-thunderbird-main-window-supernova

I am having the same problem as the person who asked the question. The message list takes up too much room. Even if there is only one message in the list, there is room for 9 messages. The dividing line below the list cannot be moved up any further. This makes the space for the email pane to be too short. I've been using Thunderbird since its inception and this is the first such problem I've had.

Well there appears to be no fix for this issue and it annoys the crap out of me. I have been with Thunderbird for several years and have been happy with it. There appears to be no purpose for this issue and most importantly the developers can't or won't fix it, and doesn't seem to be a workaround.

However, this issue has caused me to look elsewhere for an email client. Sad it got to this point as it was a great email client at one time

Thanks to all of those who tried to help

I have this same issue and it makes Thunderbird almost unusable. This really has to be fixed.