On Tue, Mar 06, 2001 at 11:49:45AM +0100, Rask Ingemann Lambertsen wrote:
 
> No. By default, Postfix scans the SMTP greeting for the string ESMTP as a
> of crude way of detecting ESMTP capability before sending HELO/EHLO, but
> obviously that's not reliable. The only way that the remote machine can tell
> you about its ESMTP capabilities is in the reply to your EHLO command.

And in fact, perusal of the relevant RFC (1869) indicates that the
presence of ESMTP in the banner should only be used to indicate that
SMTP extensions are actually implemented by that software. It is
allowable for the machine to understand only EHLO and return the same
response that HELO would return (in which case the RFC suggests that
ESMTP not be used in the banner).

The mandated behavior for ESMTP-aware clients is to issue EHLO and check
for an error response, and fall back to HELO (either after resetting the
connection or issuing an additional RSET as necessary) if indicated.

Sections 4, 7, & 8 of RFC 1869 ( http://www.rfc-editor.org/rfc/rfc1869.txt )
should be instructive for someone who wants to understand this.

-- 
Devin L. Ganger <devinthecabal.org>
A guy, his car, his miss, his nerve;
He kissed his miss and missed the curve.
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