Open the inbox from the widget instead of opening single mails only . A tap on the bar to open the inbox?
Tap on the message to go straight to it, tap the top bar to open the inbox view. Being able to do so would help users get straight to what they want without the need to pin the app and the widget on screen or tap back to go to the inbox after opening a message. This would also allow users to open the app from the widget without marking new messages as read before they're ready to actually read them.
Gernot Bacher commented
the widget has no button just to open the inbox.