RFC 1846 · EXPERIMENTAL · 1995
MON · 27 JUL 2026
SMTP 521 Reply Code
Overview
RFC 1846, “SMTP 521 Reply Code”, is an Experimental document published in September 1995 by A. Durand, F. Dupont. It has since been updated by RFC 7504. The canonical text is published by the RFC Editor.
Abstract
This memo defines a new SMTP ([1]) reply code, 521, which one may use to indicate that an Internet host does not accept incoming mail.
What “Experimental” means
Describes a specification that is part of a research or development effort, published so the community can gain experience with it.
Read this RFC
The canonical text of RFC 1846 is hosted at rfc-editor.org. Available in TXT,HTML.
Relationships to other RFCs
Other RFCs from 1995
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- RFC 1848 MIME Object Security Services
- RFC 1843 HZ - A Data Format for Exchanging Files of Arbitrarily Mixed Chinese and ASCII characters
- RFC 1842 ASCII Printable Characters-Based Chinese Character Encoding for Internet Messages
- RFC 1850 OSPF Version 2 Management Information Base
- RFC 1841 PPP Network Control Protocol for LAN Extension