("Extended TURN") An ESMTP command (first defined in RFC 1985) with which a client asks the server to deliver queued mail to the client via a new ESMTP connection. ETRN suPERsedes the SMTP "TURN" command in the same way that ESMTP' s "EHLO" suPERsedes SMTP' s "HELO". (1997-11-21)