The IESG has approved the following document: - 'SMTP 521 and 556 Reply Codes' (draft-klensin-smtp-521code-07.txt) as Proposed Standard This document has been reviewed in the IETF but is not the product of an IETF Working Group. The IESG contact person is Barry Leiba. A URL of this Internet Draft is: https://datatracker.ietf.org/doc/draft-klensin-smtp-521code/ Technical Summary This memo defines two Simple Mail Transfer Protocol (SMTP) reply codes, 521 and 556. The 521 code was originally described in an Experimental RFC in 1995 and is in wide use, but has not previously been formally incorporated into SMTP. The 556 code was created for RFC-nullMX. These codes are used to indicate that an Internet host does not accept incoming mail at all (not just under particular circumstances). This is presented for publication as a Proposed Standard, as it adds codes to RFC 5321, which is already standards track. Review and Consensus This document came out of discussions on both the apps discuss and ietf-smtp mailing lists about (1) moving RFC 1846 to the standards track, and (2) the nullMX idea. There was wide-spread agreement on both of those efforts, including accepting nullMX as an APPS WG document. The decision to create this document was mostly due to administrative ease so that there was only one document updating RFC 5321 instead of two. The nullMX document was then rewritten to point to this document. (The nullMX document has been through 10 revisions since becoming an APPS WG document.) There is widespread implementation of both of these return codes. Personnel Tony Hansen is the Document Shepherd. Barry Leiba is the responsible Area Director. This document is an individual submission.
