> So if you accidentally press something and suddenly the email is gone from your inbox, you want a toast with an undo button.
Why? If an email suddenly vanishes and you don't want that you don't need a popup to tell you what happened, you can just Ctrl-Z and the email comes back
No, not for email. Tech illiterate people use email. They're not going to have the reflex to Ctrl+Z, but a toast with "undo" at least gives them the information that undoing is possible, even if they're not quick enough to click on it
Why? If an email suddenly vanishes and you don't want that you don't need a popup to tell you what happened, you can just Ctrl-Z and the email comes back