Composing, forwarding or replying to an email? Use Alt+S to send it. You’ll notice the S is underlined on the Send button. That means it performs that function with the Alt key.
Substitute Alt+. (period) when you don’t want to click in the To: line when composing an email. Sometimes, you just start typing your message and then later you think about addressing it. Just click Alt+. (period).
Toggle to the Subject line in an email message by hitting Alt+U. If you want to add or change the subject line when you're in the body of the email, Alt+U will get you up to the field. Just tab to return to the body.