Tip #17
How to turn off viewing next message in Apple Mail

If you're an Apple Mail user who gets annoyed when the app opens the next email after deleting or archiving, I have good news for you: there's a setting you can toggle. FYI - you'll need to toggle the setting for each device.
There are many reasons you might want to do this. You may simply not want to advance to a new email because you're not ready to read it. You might also be able to tell it's junk right off the bat and don't want to load any tracking pixels by opening it. Whatever your reasons are, here's how you do it.
Mac
Uncheck the box at Settings > Viewing > Automatically view next messsage after discarding or archiving message.
iOS and MacOS
Choose Don't Select a Message in the Settings app under Apps > Mail > Delete or Move Message Action.