I posted this in your other thread. How do I move to next email from an open email? Little arrows have - Microsoft Community
When you view messages in a separate window, the Next and Previous arrows are only available on the Quick Access Toolbar.
The Quick Access Toolbar can be above or below the ribbon.
First, open a message.
Make the Quick Access Toolbar appear. (first picture)
Click on the Customize Quick Access Toolbar icon at the end of the bar. (second picture)
Click More Commands.
Add Next and Previous. (third picture)
Another way to get to the Customize page:
First, open a message.
File > Options > Quick Access Toolbar
Note: you have to use the File menu from an open message.


