2007-04-27 2015-12-18 RFC Required SEND REPORT AUTH NICKNAME RFC Required To-Path From-Path Message-ID Success-Report Failure-Report Byte-Range Status Expires Min-Expires Max-Expires Use-Path WWW-Authenticate Authorization Authentication-Info Use-Nickname RFC Required 200 Success 400 Unintelligible 401 Unauthorized 403 Action-not-allowed 404 Failure to resolve recipient's URI 408 Transaction-did-not-complete-in-allotted-time 413 Stop-sending-message 415 MIME-not-understood 423 Parameter-out-of-bounds 424 Malformed nickname 425 Nickname reserved or already in use 428 Private messages not supported 481 Session-does-not-exist 501 Request-method-not-understood 506 Session-already-in-use