Using different swipe depths (e.g., <50% and ≥50%) in the mail view could enable quick access to four distinct actions, such as marking as read/unread, starring, moving, or deleting emails.
To clarify what I mean:
When swiping from left to right, the action would depend on the swipe depth: If the swipe is less than halfway across the screen, the action might be to mark the email as read/unread. Then, If the swipe goes beyond the halfway point, the action could switch to deleting the email.
If only one action is chosen in the settings for either direction, the behaviour would remain as it is now, allowing for more actions for those who want it.
This is inspired by some messaging apps I've used that offer different actions depending on how far a chat is swiped. I believe applying a similar idea to emails would be a handy addition.