I spent two days thinking the login feature was broken on the app. If I tapped on the "login first" popup it didn't take me to a login, it just behaved like I was tapping whatever was underneath the popup.
Took me a long time and i even had to ask if logins are supported in the app.
If I was the developer, I would change the login experience and the long hold on mail header to see mail action icons... Those things are really weird.