This memo splits message submission from message relay@ allowing each service to operate according to its own rules (for security@ policy@ etc.)@ and specifies what actions are to be taken by a submission server. Message relay is unaffected@ and continues to use SMTP over port 25. When conforming to this document@ message submission uses the protocol specified here@ normally over port 587. This separation of function offers a number of benefits@ including the ability to apply specific security or policy requirements.