I'm sorry but it isn't as obvious as you think and I have the right to ask questions or discuss something I may not have made an involved study of.  I haven't worked much with these settings.  The check box about closing the window or tab is not checked in my program and it never has been.  But when I delete a message and I'm using the display messages in the same window, the window closes.  I haven't experimented to see what happens using the other settings.

Also, from discussions I've seen on other lists, if you use another setting, not the display messages in the same window setting, it appears you can't use escape to close a message after reading it. 

I was asking what happens if you use delete in an opened message using various settings.  You did not answer the question.  If you haven't tried this, you don't know.

It would seem logical that if the check box is unchecked and you press delete on an opened message where new messages open in a different tab or not in the same window, that the tab or window might not close and the message may not be deleted.  But unless you try these different settings, you don't know. 

At times people, including you, ask about something without doing tests or looking up information.  I did not believe I had to test these different settings with the check box checked and unchecked before asking the question. 

I can't speak about sighted users, but it appears to me that for blind users, the have messages open in the same window is the best setting to use.

Asking what these settings do is not being obtuse or a pain in the ass.

Gene