About Supersedes
https://de.wikipedia.org/wiki/Canceln
https://en.wikipedia.org/wiki/Control_message#cancel
https://de.wikipedia.org/wiki/Supersede
https://www.rfc-editor.org/rfc/rfc822.txt
1.1. SCOPE
This standard specifies a syntax for text messages that are
sent among computer users, within the framework of "electronic
mail". The standard supersedes the one specified in ARPANET
Request for Comments #733, "Standard for the Format of ARPA Net-
work Text Messages".
A.1.2. Neuman@BBN-TENEXA
These two "Alfred Neuman" examples have identical seman-
tics, as far as the operation of the local host's mail sending
(distribution) program (also sometimes called its "mailer")
and the remote host's mail protocol server are concerned. In
the first example, the "Alfred Neuman" is ignored by the
mailer, as "Neuman@BBN-TENEXA" completely specifies the reci-
pient. The second example contains no superfluous informa-
tion, and, again, "Neuman@BBN-TENEXA" is the intended reci-
pient.
Note: When the message crosses name-domain boundaries, then
these specifications must be changed, so as to indicate
the remainder of the hierarchy, starting with the top
level.
https://www.rfc-editor.org/rfc/rfc1123.txt
ELECTRONIC MAIL -- SMTP and RFC-822
5.1 INTRODUCTION
In the TCP/IP protocol suite, electronic mail in a format
specified in RFC-822 [SMTP:2] is transmitted using the Simple Mail
Transfer Protocol (SMTP) defined in RFC-821 [SMTP:1].
While SMTP has remained unchanged over the years, the Internet
community has made several changes in the way SMTP is used. In
particular, the conversion to the Domain Name System (DNS) has
caused changes in address formats and in mail routing. In this
section, we assume familiarity with the concepts and terminology
of the DNS, whose requirements are given in Section 6.1.
RFC-822 specifies the Internet standard format for electronic mail
messages. RFC-822 supercedes an older standard, RFC-733, that may
still be in use in a few places, although it is obsolete. The two
formats are sometimes referred to simply by number ("822" and
"733").
