Claus Assmann:
> On Thu, Sep 30, 2010, Victor Duchovni wrote:
>
> > Do you have a tcpdump capture? From the above it sounds like HELO is
> > sent before the 220 banner. That's a protocol error.
>
> Is it?
>
> 4.3.1 Sequencing Overview
> ...
> One important reply is the connection greeting. Normally, a receiver
> will send a 220 "Service ready" reply when the connection is
> completed. The sender SHOULD wait for this greeting message before
> sending any commands.
>
> So this is "just" a SHOULD, not a MUST, hence not a protocol error
> per se. Any real MTA will obey the SHOULD requirement of course.
Also, multi-line 220 greetings are not documented up to RFC 2821,
but they have been in use for more than 15 years; and "hangup after
521" is still not officially blessed, but postscreen will send it
to get rid of clients immediately (smtpd has supported this as of
Postfix 2.6).
These features don't appear to hamper inter-operability with
well-behaved MTAs (and the more sites deploy these features,
the less likely legitimate mail is to break).
Wietse
