Conformance for the M-Switch ACP127 and M-Switch Encryption add-ons as well as for the M-Switch Constrained Network Server and Gateway, which are additional to the Open Standards listed below, can be found on the product pages for those products and add-ons.

RFC 1123 Requirements for Internet hosts - application and support. R. Braden, October 1989
RFC 1870 SMTP Service Extension for Message size Declaration. J. Klensin, N. Freed, K. Moore, November 1995
RFC 2033 Local Mail Transfer Protocol. J. Meyers, October 1996
RFC 2034 SMTP Service Extension for Returning Enhanced Error Codes. N. Freed, October 1996
RFC 2045 Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies. N. Freed, N. Borenstein, November 1996
RFC 2046 Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types. N. Freed, N. Borenstein, November 1996
RFC 2047 Multipurpose Internet Mail Extensions (MIME) Part Three: Header Extensions for Non-ASCII Text. K. Moore, November 1996
RFC 2049 Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples. N. Freed, N. Borenstein, November 1996
RFC 2231 MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations. N. Freed, K. Moore, November 2007
RFC 2369 The Use of URLs as Meta-Syntax for Core Mail List Commands and their Transport through Message Header Fields. G. Neufeld and J. Baer, July 1998
RFC 2505 Anti-Spam Recommendations for SMTP MTAs. G. Lindberg, February 1999
RFC 2634 Enhanced Security Services for S/MIME. P. Hoffman, June 1999
RFC 2852 Deliver By SMTP Service Extension, D. Newman, June 2000
RFC 2919 List-Id: A Structured Field and Namespace for the Identification of Mailing Lists. R. Chandhok and G. Wenger, March 2001
RFC 2920 SMTP Service Extension for Command Pipelining. N. Freed, September 2000
RFC 3030 SMTP Service Extensions for Transmission of Large and Binary MIME Messages. G. Vaudreuil, December 2000
RFC 3207 SMTP Service Extension for Secure SMTP over Transport Layer Security. P. Hoffman, Feb 2002
RFC 3461 Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs). K. Moore, January 2003
RFC 3798 Message Disposition Notification. T. Hansen, Ed & G. Vaudreuil, May 2004
RFC 3848 ESMTP and LMTP Transmission Types Registration. C. Newman, July 2004
RFC 4468 Message Submission BURL Extension. C. Newman, May 2006
RFC 4865 SMTP Submission Service Extension for Future Message Release. G. White and G. Vaudreuil, May 2007
RFC 4954 SMTP Service Extension for Authentication. R. Siemborski, A. Melnikov, July 2007
RFC 5321 Simple Mail Transfer Protocol. J. Klensin, October 2008
RFC 5322 Internet Message Format. P. Resnick, Ed, October 2008
RFC 5550 The Internet Email to Support Diverse Service Environments (Lemonade) Profile. D. Cridland, A. Melnikov, S. Maes, August 2009
RFC 5652 Cryptographic Message Syntax (CMS). R. Housley, September 2009
RFC 5751 Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification. B. Ramsdell, January 2010
RFC 5753 Use of Elliptic Curve Cryptography (ECC) Algorithms in Cryptographic Message Syntax (CMS)). S. Turner, D. Brown, January 2010
RFC 6152 SMTP Service Extension for 8-bit MIME transport. J. Klensin, N. Freed, M. Rose, E. Stefferud, D. Crocker, March 2011
RFC 6376 DomainKeys Identified Mail (DKIM) Signatures. D. Crocker, T. Hansen, M. Kucherawy, September 2011
RFC 6409 Message Submission for Mail. R. Gellens & J. Klensin, November 2011
RFC 6477 Registration of Military Message Handling System (MMHS) Header Fields for Use in Internet Mail. A. Melnikov & G. Lunt, January 2012
RFC 6522 The Multipart/Report Media Type for the Reporting of Mail System Administrative Messages. M. Kucherawy, January 2012
RFC 6710 Simple Mail Transfer Protocol Extension for Message Transfer Priorities. A. Melnikov and K. Carlberg, August 2012
RFC 6758 Tunneling of SMTP Message Transfer Priorities. A. Melnikov, K. Carlberg, October 2012
RFC 7001 Message Header Field for Indicating Message Authentication Status. M. Kucherawy, September 2013
RFC 7444 Security Labels in Internet Email. A. Melnikov, K. Zeilenga, February 2015
RFC 7912 Message Authorizing Email Header Field and Its Use for the Draft and Release Procedure
draft-melnikov-smime-header-signing Considerations for protecting Email header with S/MIME. A. Melnikov, June 2016

In addition to the above M-Switch X.400 supports ACP142 (Version 1.0) "P_MUL - A Protocol for Reliable Multicast Messaging in Bandwidth Constrained and Delayed Acknowledgement (EMCON) Environments" for use with Data Diodes only. ACP142 for use in constrained cetwork environments is supported in the M-Switch Constrained Network products.