| 1845 | SMTP Service Extension for Checkpoint/RestartD. Crocker, N. Freed, A. Cargille | Experimental | September 1995 |
| 1870 | SMTP Service Extension for Message Size DeclarationJ. Klensin, N. Freed, K. Moore | Internet Standard | November 1995 |
| 1950 | ZLIB Compressed Data Format Specification version 3.3P. Deutsch, J-L. Gailly | Informational | May 1996 |
| 2034 | SMTP Service Extension for Returning Enhanced Error CodesN. Freed | Proposed Standard | October 1996 |
| 2119 | Key words for use in RFCs to Indicate Requirement LevelsS. Bradner | Best Current Practice | March 1997 |
| 2442 | The Batch SMTP Media TypeN. Freed, D. Newman, J. Belissent, M. Hoy | Informational | November 1998 |
| 2852 | Deliver By SMTP Service ExtensionD. Newman | Proposed Standard | June 2000 |
| 2920 | SMTP Service Extension for Command PipeliningN. Freed | Internet Standard | September 2000 |
| 3030 | SMTP Service Extensions for Transmission of Large and Binary MIME MessagesG. Vaudreuil | Proposed Standard | December 2000 |
| 3207 | SMTP Service Extension for Secure SMTP over Transport Layer SecurityP. Hoffman | Proposed Standard | February 2002 |
| 3461 | Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs)K. Moore | Draft Standard | January 2003 |
| 3464 | An Extensible Message Format for Delivery Status NotificationsK. Moore, G. Vaudreuil | Draft Standard | January 2003 |
| 3865 | A No Soliciting Simple Mail Transfer Protocol (SMTP) Service ExtensionC. Malamud | Proposed Standard | September 2004 |
| 4141 | SMTP and MIME Extensions for Content ConversionK. Toyoda, D. Crocker | Proposed Standard | November 2005 |
| 4405 | SMTP Service Extension for Indicating the Responsible Submitter of an E-Mail MessageE. Allman, H. Katz | Historic | April 2006 |
| 4468 | Message Submission BURL ExtensionC. Newman | Proposed Standard | May 2006 |
| 4954 | SMTP Service Extension for AuthenticationR. Siemborski, Ed., A. Melnikov, Ed. | Proposed Standard | July 2007 |
| 5234 | Augmented BNF for Syntax Specifications: ABNFD. Crocker, Ed., P. Overell | Internet Standard | January 2008 |
| 5321 | Simple Mail Transfer ProtocolJ. Klensin | Draft Standard | October 2008 |
| 5322 | Internet Message FormatP. Resnick, Ed. | Draft Standard | October 2008 |
| 5598 | Internet Mail ArchitectureD. Crocker | Informational | July 2009 |
| 5750 | Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Certificate HandlingB. Ramsdell, S. Turner · obsoleted by RFC 8550 | Proposed Standard | January 2010 |
| 5751 | Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message SpecificationB. Ramsdell, S. Turner · obsoleted by RFC 8551 | Proposed Standard | January 2010 |
| 6152 | SMTP Service Extension for 8-bit MIME TransportJ. Klensin, N. Freed, M. Rose, D. Crocker, Ed. | Internet Standard | March 2011 |
| 6409 | Message Submission for MailR. Gellens, J. Klensin | Internet Standard | November 2011 |
| 6522 | The Multipart/Report Media Type for the Reporting of Mail System Administrative MessagesM. Kucherawy, Ed. | Internet Standard | January 2012 |
| 6710 | Simple Mail Transfer Protocol Extension for Message Transfer PrioritiesA. Melnikov, K. Carlberg | Proposed Standard | August 2012 |
| 6713 | The 'application/zlib' and 'application/gzip' Media TypesJ. Levine | Informational | August 2012 |
| 7293 | The Require-Recipient-Valid-Since Header Field and SMTP Service ExtensionW. Mills, M. Kucherawy | Proposed Standard | July 2014 |
| 7601 | Message Header Field for Indicating Message Authentication StatusM. Kucherawy · obsoleted by RFC 8601 | Proposed Standard | August 2015 |
| 7841 | RFC Streams, Headers, and BoilerplatesJ. Halpern, Ed., L. Daigle, Ed., O. Kolkman, Ed. | Informational | May 2016 |
| 8126 | Guidelines for Writing an IANA Considerations Section in RFCsM. Cotton, B. Leiba, T. Narten | Best Current Practice | June 2017 |
| 8174 | Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsB. Leiba | Best Current Practice | May 2017 |