Re: [Exim] hiding software type & version

On Mon, 23 Dec 2002, Dennis Davis wrote:

> >smtp_banner = "${primary_hostname} ESMTP Server ready."
> >
> >IIRC a server SHOULD announce that it understands ESMTP.
> >There was a discussion on exim-users some months ago.
>
> I'll take that as SHOULD as usually defined in the RFCs and not a
> MUST as defined in the RFCs. I find little mention of using ESMTP
> in the banner greeting of an SMTP server in the appropriate RFC. My
> reading of RFC2821 indicates that a client should determine what, if
> any extensions are supported, by the response to an EHLO command.
> And should even be prepared to have the EHLO command not recognised
> and fall back to using the HELO command [1].
>
> Please correct me in I'm wrong, but we've received no complaints
> about the use of SMTP, instead of ESMTP, in our banner greetings.
> No-one has complained that this has stopped them talking to us.
> Certainly mail on this list gets through to me OK despite having to
> pass through such anachronistic mail servers :-)

Well, I think most mailers just start with EHLO, and if this is rejected,
they fall back to HELO.

Exim itself checked for the ESMTP string in the banner in older versions
(read Philip's comment in line 776 in transports/smtp.c) and used HELO if
no ESMTP string was announced.

I wouldn't be surprised if some other mailers still run plain SMTP if no
ESMTP is in the banner string.

ciao