: "Sign in to Outlook (Hotmail)" covers both the current platform name and the legacy domain.
: The addition of "sign in" makes the call-to-action clear. It is better than just "@hotmail.com" because it specifies the action required. Suggested Refinements @hotmail.com sign in
: "Sign in to Hotmail" or "Hotmail Login" is more standard for UI. : "Sign in to Outlook (Hotmail)" covers both