Hi people,
For STD 10, RFC 1869, SMTP Service Extensions, it is not made clear,
except possibly in a pair of examples provided by that memo, exactly
whether or not the commands defined as optional and not required for a
minimum implementation of SMTP (RFC 821), should or should not be
advertised as described by the Service Extensions listings maintained by
IANA in the manner described by RFC 1869. In fact, no mandates are set
upon the specific advertisement of any service, be it supported or not, of
RFC 821 origin or otherwise. Specifically, since the standard
implementation of SMTP in RFC 821 makes no requirement for advertising
optional commands that may be implemented (HELP, EXPN, SAML, SOML, etc),
is it a violation of RFC 1869 that the server, despite supporting those
features of RFC 821, does not advertise any or some of those supported
commands in the ESMTP ehlo response, even if they are available for
service in normal use of SMTP? Since they were defined as extensions only
when the extensions framework was built, it seems unreasonable to expect
implementations which may support the ESMTP framework to necessarily
advertise those commands, rather than the few new ESMTP extensions such as
Auth and StartTLS that the framework support was probably designed to
cater for and for which developers have incorporated support into their
mail transports. Not advertising features of SMTP will slightly decrease
the transaction overhead without impact, in all probability, since the
assumption can safely be made that those esoteric features of SMTP that
are of any use to a specific client are called usually with prior
knowledge of the features provided by the server, as in the use of turn or
help in normal RFC 821 usage. Finally, many SMTP services out there
exhibit this exact behaviour, not advertising supported features of SMTP
in their ESMTP synopsis, so it is of interest to me to know whether, as
part of the configurability of a mail transport, the option to advertise
any, all, or all except RFC821 specific optional commands should be made
available, or even whether or not the advertising of any service, of
whatever origin, is required at all in any case. The help verb may then
list all verbs which are supported, inclusive of those defined by RFC 821
or otherwise excluded for administrative reasons.
What are your thoughts?
Cheers,
Sabahattin
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