Don't lose your mail: FastMail on the web
Except you didn't lose your email, because the web interface will check with you if you try to delete lots of messages in one go (accidentally clicking on "select all" before clicking "delete") and require for you to confirm this is really what you meant to do.
And even if you did delete mail you meant to keep, you can use our keyboard shortcuts to undo the delete and your mail returns safely. You can go about your day, happy.
But then you notice there's other mail missing. You only just noticed and undo isn't helping (perhaps your mail was deleted through a mail client or on the web last week), but it's gone and now you need it back.