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2009-01-29 12:08:08

I was taking Tony Finch's comments

        But there's plenty of other information that the server has to
        discard - for example any AUTH results, any partial MAIL
        transactions - which isn't explicitly listed in RFC 3207.

to its next step. He was saying that

        S: <start>
        C: 220
        S: MAIL FROM:<...>
        C: 250 OK
        S: RCPT TO:<...>
        C: 250 OK
        S: STARTTLS

that the MAIL_FROM and RCPT_TO information is also discarded. So my
observation was that

        STARTTLS SHOULD only be executed immediately after the initial

Doing otherwise may cause the server to do extra processing that will
all just get thrown away.

The verbs that I gave examples of were ones that don't affect the state
machine in any way, so would be reasonable to send between <start> and
STARTTLS. That's why I said "SHOULD" instead of "MUST".

I'm going to suggest an Errata in a separate email message.


John C Klensin wrote:

--On Thursday, January 29, 2009 10:09 -0500 Tony Hansen
<tony(_at_)att(_dot_)com> wrote:

If this is the interpretation that we gain consensus on, that
it means "start over from scratch", it might as well also say
that it

     SHOULD only be executed immediately after the initial EHLO.

The only possible exceptions to this rule would be for verbs
that don't affect the state machine, such as VRFY, EXPN, HELP,

RSET is also harmless immediately after EHLO.  Changing the
state from "session open (EHLO issued), no mail transaction
state" to "session open (EHLO issued), no mail transaction
state" is a no-op.  And the first paragraph of of 5321
says that.

Out of context, I'm not sure exactly what you are suggesting
above, but I believe that it would mean:

    S: 220 ...
    C: EHLO ...
    S: 250-...
    S: 250-STARTTLS
    S: 250-...
    S: 250 OK
    C: STARTTLS  ...
    (TLS session starts)
    and the next command must be either EHLO
    or as many instances of any of VRFY, 
      EXPN, HELP, NOOP, RSET as desired, followed by EHLO

Also, the "what the server MUST (or SHOULD) discard and the
client MUST (or SHOULD) not depend on" sentences and example
might reasonably be modified to explicitly include any
information gained from VRFY or EXPN issued between the 220
greeting and the initial EHLO.  While one might not trust VRFY
or EXPN queries or results issued under TLS either, it would be
pointless and silly to send them before the initial EHLO if one
knew that one was going to issue STARTTLS if the server
permitted it.   Indeed the only reason for doing so would be if
one intended to make a decision about whether to continue with a
mail transaction at all based on the results of VRFY or EXPN...
and that would be very rare today except in special