SMTP service
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This memo defines a framework for extending the SMTP service by
defining a means whereby a server SMTP can inform a client ...
... SMTP as to
the service extensions it supports. Extensions to the SMTP service
are registered with the IANA. This framework ...
... SMTP is widely and robustly deployed, some parts of the
Internet community might wish to extend the SMTP service. This memo
defines a means whereby both an extended SMTP client and server ...
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It must be emphasized that any extension to the SMTP service should
not be considered lightly. SMTP's strength comes primarily from its
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... deployment, and interoperability costs. In many cases, the cost of
extending the SMTP service will likely outweigh the benefit.
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... a registry of SMTP service extensions (section 5) ...
... EHLO command instead of the HELO command. If
the SMTP server supports the SMTP service extensions it will give a
successful response (see section 4.3), a failure response (see 4.4),
or an error response ...
... error response (4.5). If the SMTP server does not support any
SMTP service extensions it will generate an error response (see
section 4.5).
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... The IANA maintains a registry of SMTP service extensions. Associated
with each such extension is a corresponding EHLO keyword value. Each
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... the textual name of the SMTP service extension;
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... EHLO keyword value that starts with an upper or
lower case "X" refers to a local SMTP service extension, which is
used through bilateral, rather than standardized, agreement. Keywords
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... IESG-
approved experimental SMTP service extension registered with IANA. A
conforming server must not offer non "X" prefixed keyword values that
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If the server SMTP determines that the SMTP service is no longer
available (e.g., due to imminent system shutdown), it will return
code 421.
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... headers of all messages they receive. A "with ESMTP" clause
should be added to this field when any SMTP service extensions are
used. "ESMTP" is hereby added to the list of standard protocol names
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... C: <open connection to server>
S: 220 dbc.mtview.ca.us SMTP service ready
C: EHLO ymir.claremont.edu
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... C: <open connection to server>
S: 220 dbc.mtview.ca.us SMTP service ready
C: EHLO ymir.claremont.edu
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... service extensions (XONE and XVRB).
(3) Finally, a server that does not support SMTP service
extensions would act as follows:
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... C: <open connection to server>
S: 220 dbc.mtview.ca.us SMTP service ready
C: EHLO ymir.claremont.edu
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