An SMTP MAY implement the commands to send a message to a user's terminal: SEND, SOML, and SAML.
It has been suggested that the use of mail relaying through an MX record is inconsistent with the intent of SEND to deliver a message immediately and directly to a user's terminal. However, an SMTP receiver that is unable to write directly to the user terminal can return a "251 User Not Local" reply to the RCPT following a SEND, to inform the originator of possibly deferred delivery.