2013-04-07 RFC5321, Section 2.2 Standards-Track or IESG-Approved Experimental RFC The Simple Mail Transfer Protocol specifies a set of commands or services and a general procedure for extending that set. The table below lists SMTP service extensions. Both message submission and mail transfer may use these extensions unless otherwise specified. As specified in Section 2.2.2, no entry may be made in this registry that starts in an "X". Entries may be made only for service extensions (and associated keywords, parameters, or verbs) that are defined in Standards-Track or Experimental RFCs specifically approved by the IESG for this purpose. The server response to a client EHLO command includes a keyword for each service extension the server implements. Some of these keywords have parameters, which are listed in the "SMTP Service Extension Parameters" registry. SEND Send as mail The description of SEND was updated by and then its actual use was deprecated in SOML Send as mail or to terminal The description of SOML was updated by and then its actual use was deprecated in SAML Send as mail and to terminal The description of SAML was updated by and then its actual use was deprecated in EXPN Expand the mailing list Command description updated by HELP Supply helpful information Command description updated by TURN Interchange the client and server roles The actual use of TURN was deprecated in 8BITMIME SMTP and Submit transport of 8bit MIME content SIZE Message size declaration VERB Verbose Eric Allman ONEX One message transaction only Eric Allman CHUNKING Chunking BINARYMIME Binary MIME CHECKPOINT Checkpoint/Restart DELIVERBY Deliver By PIPELINING Command Pipelining DSN Delivery Status Notification ETRN Extended Turn SMTP only. Not for use on Submit port 587. ENHANCEDSTATUSCODES Enhanced Status Codes STARTTLS Start TLS NO-SOLICITING Notification of no soliciting MTRK Message Tracking SUBMITTER SMTP Responsible Submitter ATRN Authenticated TURN SMTP only. Not for use on Submit port 587. AUTH Authentication BURL Remote Content Submit only. Not for use with SMTP on port 25. FUTURERELEASE Future Message Release UTF8SMTP Internationalized email address Experimental; deprecated in . CONPERM Content Conversion Permission CONNEG Content Conversion Negotiation SMTPUTF8 Internationalized email address MT-PRIORITY Priority Message Handling RFC5321, Section 2.2 Standards-Track or IESG-Approved Experimental RFC Some of the keywords in the "SMTP Service Extensions" registry have parameters. These are listed here (those keywords not listed here have no parameters). SIZE number NO-SOLICITING Soliciting-keywords AUTH SASL mechanism names BURL Permitted URL prefixes MT-PRIORITY Name of the Priority Assignment Policy (optional) Standards-Track or IESG-Approved Experimental RFC The Simple Mail Transfer Protocol and the Standard for the Format of ARPA Internet Text Messages specify that a set of "Received" lines will be prepended to the headers of electronic mail messages as they are transported through the Internet. These received line may optionally include either or both a "via" phrase and/or a "with" phrase. The legal values for the phrases are listed here. The via phrase is intended to indicate the link or physical medium over which the message was transferred. The with phrase is intended to indicate the protocol or logical process that was used to transfer the message. UUCP Unix-to-Unix Copy Program TCP TCP SMTP Simple Mail Transfer Protocol ESMTP SMTP with Service Extensions ESMTPA ESMTP with AUTH ESMTPS ESMTP with STARTTLS ESMTPSA ESMTP with both STARTTLS and AUTH LMTP Local Mail Transfer Protocol LMTPA LMTP with AUTH LMTPS LMTP with STARTTLS LMTPSA LMTP with both STARTTLS and AUTH MMS Multimedia Messaging Service UTF8SMTP ESMTP with SMTPUTF8 UTF8SMTPA ESMTP with SMTPUTF8 and AUTH UTF8SMTPS ESMTP with SMTPUTF8 and STARTTLS UTF8SMTPSA ESMTP with SMTPUTF8 and both STARTTLS and AUTH UTF8LMTP LMTP with SMTPUTF8 UTF8LMTPA LMTP with SMTPUTF8 and AUTH UTF8LMTPS LMTP with SMTPUTF8 and STARTTLS UTF8LMTPSA LMTP with SMTPUTF8 and both STARTTLS and AUTH Standards-Track or IESG-Approved Experimental RFC PRIORITY Records the value of the MT-PRIORITY parameter specified in the MAIL FROM command See Section 7 of RFC state Indicates entry into a special queue state state <state-name> Specification Required MIXER Default policy RFC6710, Appendix B STANAG4406 RFC6710, Appendix A NSEP RFC6710, Appendix C First Come First Served auth Held for message authentication current content Held for message content analysis current convert Held for message content conversion current moderation Held for list moderation current normal Message is not being held other than to accommodate typical relaying handling current other Held for causes not covered by other registered state keywords current outbound Message placed in outbound queue current quarantine Held for operator action due to content analysis or local policy current timed Held to accommodate a specific requested delivery window current