RFC 7504: SMTP 521 and 556 Reply Codes

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…

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Outgoing relationships (4 related RFCs)

Updates, Normative reference — RFC 5321: Simple Mail Transfer Protocol
Updates, Informative reference — RFC 1846: SMTP 521 Reply Code
Normative reference — RFC 2119: Key words for use in RFCs to Indicate Requirement Levels
Informative reference — RFC 7505: A "Null MX" No Service Resource Record for Domains That Accept No Mail

Incoming relationships (1 related RFC)

Normatively referenced by — RFC 7505: A "Null MX" No Service Resource Record for Domains That Accept No Mail