Found 1 record.

Status: Verified (1)

RFC 1985, "SMTP Service Extension for Remote Message Queue Starting", August 1996

Errata ID: 4130
Status: Verified
Type: Editorial
Publication Format(s) : TEXT
Reported By: Michael Slusarz
Date Reported: 2014-10-13
Verifier Name: Barry Leiba
Date Verified: 2014-10-14

Section 5.2 says:

If one of the 500 level error codes (550 or 551) are sent, the client
should assume that the protocol is not supported in the remote host
or that the protocol has not been implemented correctly on either the
client or server host. 

It should say:

If one of the 500 level error codes (500 or 501) is sent, the client
should assume that the protocol is not supported in the remote host
or that the protocol has not been implemented correctly on either the
client or server host. 

Notes:

550 (mailbox unavailable) and 551 (user not local) are clearly not the codes intended here; this text is meant to refer to the two syntax error codes specified in Section 5.1.

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