What does the ! icon do?

[gandalfmeister]

..when reading a message you get the ! icon (as well as the delete , reply etc) - what does this icon do?
I pressed it - and an email I was reading simply disappeared!

[Kostya Vasilyev]

What is the ! icon?

Do you have a screenshot?

Is it the leftmost icon in the icon bar?

That's delete (one of "move to deleted" / "delete now" / "hide in the app, keep on the server", depending on how you've configured the account... the default is "move to deleted").