IOS iPad email

The icon that you describe mere triggers display of the Mail Shelf (the Shelf being a new feature of iPadOS multitasking environment). Tapping the icon summons the shelf view - which will show you a thumbnail image of all the running instances of the Mail App. Where multiple instances are running, a simple tap of a thumbnail will instantly switch to that view.

The iPadOS multitasking environment permits you to run multiple “instances” of the same App, such as Mail - with each instance, perhaps having a different open inbox.

For example, if you have three running instances of Mail, tapping the icon you describe will open the shelf with three thumbnails - each corresponding to each running instance of Mail. Simply tapping a thumbnail will switch directly to that running instance of the Mail App.

This article from Appleinsider has a useful explanation of this new feature along with many of the updates to multitasking:

https://appleinsider.com/articles/21/08/12/how-to-master-multitasking-on-ipad-and-ipad-pro-in-ipados-15

The iPad User Guide is also a rich source of frequently overlooked information. The Guide is available both online using a web browser (such as Safari), or as an Apple Books download:

iPad User Guide - Apple Support

https://books.apple.com/book/id1567104892

Hi jcasey555,

Welcome to the Apple Support Communities!

We are happy to help with the issue you are having with wanting to know what the icon at the bottom of your "all inboxes window" is. Could you post a photo showing what the box looks like so that we can better help?

Cheers!

You are very welcome.