But in the reading panel, where you can actually see the message contents, the swipe actions are hardwired - scroll in conversation, or go to next conversation. This is less good.
I am a big fan of apps like Zero.app and Triage.app, that allow me to do my most common actions via swipes when I am looking at a screen where much of the message can be read - more than the preview in the message list.
My most common actions are read, dispose of (I archive, not delete), or skip and move to next/previous.
It is easier to swipe, eg swipe up, to archive, which I can do in Triage and Zero, than it is to poke the archive icon. Especially than to poke the tiny icon on my iPhone screen (easier on my iPad), when using Outlook.app in landscape mode with list and reading panes side by side. Or to swipe the current message in the message list (which, by the way, is hard to tell apart from the other messages - you should have a better color scheme. I often end up at giving the wrong message when I have to go back to the message list)
Much easier to swipe than it is to switch back to list on another screen, in portrait mode.
In portrait mode, you should be able to swipe to archive or move on, right on the message which occupies most of the screen.
Think about it: the most frequent operations need to be the easiest to do. Or, the classic GUI / UI / UX principle of direct manipulation: if I want to archive a message, I want to manipulate it directly, in the message reading panel, not indirectly, in the message list (which may be on a different screen)
In fact, I had completely given up on Outlook.app, and have been using only Zero.app, because I found that I could process my email much faster in Zero.app. Typically one swipe per message in Zero. But, by my count, 4 taps or swipes in Outlook.app
The only reason I am trying out Outlook.app again are
1) my company no longer allows IMAP access to our Exchange server, so I can no longer use Zero.app for work email, only personal
2) I bought an iPad mini, where tapping to archive button is less error prone.
Along the way: even with the current inefficient interface, I want to be able to archive and move on to view the next message. The current interface in landscape mode often shows a blank message reading pane after I archive, requiring me to painfully select a new message to look at.
You really need to count the number of actions - pokes, clicks, taps, swipes - to get the job of processing email done. Swipes are about 2x better, or half the cost, of poking or tapping an icon or widget. Switching screens is about 2x worse than tapping an icon, 4x worse than a swipe. Simple swipes left / right / up / down are fastest; long vs short swipes are almost as good, maybe 10-20% worse than a simple swipe; multiple buttons, one of which must be tapped, is maybe 50% worse, but still better than having to tap an icon or widget that may be far away (the swipe equivalent of context menus)