Interface and icon usage
When I disable "show message detail" and only look at my list of emails, there is no easy way to delete an email other than swiping left or right. It would be nice to have hover icons (that appear when you hover) to the right of the "unread" and "star" indicators.
In this same view, if I double click an email to open it, the message will appear in a new window (as expected). However, this window does not contain any customizable icons. One major issue is that there is no "trash" icon. So it's hard to double-click an email with my mouse and delete it right away with my mouse. The only way I can think of is to press a key on the keyboard. This slows down my workflow.
If, however, I have set "show message detail" to be on, a new banner of icons appears above each message, but this row of icons is not appearing when emails are opened in their individual windows. This is an interface inconsistency.
Another inconsistency is the way icons are presented for received emails vs. how icons are presented for an email you're in the middle of composing. When I'm composing a new message, I have small, beautiful icons to the left of the "Save" and "Send" buttons and they allow me to do all kinds of cool things like delay-send an email. However, when I double click an email to open it in its own window, the icons (e.g. reply, reply all) look different in size and style from the ones in the compose window, and they are placed in a different place. And lastly, as I already pointed out - the icon bar on top of each received message that appears when you turn on the "show message detail" view is also inconsistent with these other two views.
Please do some interface cleanup to make all these things more consistent and tidy. Consider adding hover icons in the message list view.