Email Message Preview Window: Bottom Handle Stuck at the Bottom

Well, I've done this before and remedied it by accident. The issue is that I used the bottom t-handle to expose more of the list of emails and... the preview of the last selected email disappeared with said handle now stuck at the bottom and previews cannot be seen. Period.

I'm using Mojave 10.14.6 because it works for me.

Here's a screen grab of the bottom of the window. When I hover, click and hold the dot at the bottom until t-handle appears, it will not budge not matter what I do. No resizing the window drastically (as mentioned in other posts)... nothing.

Thanks in advance for your suggestions.

Brad