I was wondering if it wouldn't be smart to use an extension to EHLO as a
way to detect QMTP availability on an MX. I decided to check and 'QMTP'
& 'EHLO' only appear together 4 times. Chuck Foster seems to be the
first to have asked whether it wouldn't be smart to add a "250 QMTP"
(later corrected to "250 XQMTP" by L. Widdifield) to the EHLO response.
Janos Farkas felt that this (rightfully) adds a couple round-trips at
least to the communication, instead of reducing it as much as QMTP does
by definition. At this point the discussion died.
However, isn't it worth having some method in place for actually using
this more efficient protocol? The round-trips required by "Mail from:"
and "Rcpt To:" and "Data" are all eliminated, and the "250 XQMTP" could
be given as the first 250 response, allowing the QMTP compatible MTA to
immediately send a confirmation, not reading / parsing the remainder of
the TCP stream (which may be a slight improvement).
{ Syntax: "<" from server ... ">" to server }
< 220 IP ESMTP
> EHLO
< 250 IP
< 250 XQMTP
> QMTP
> (data stream)
< (response)
I see this as adding two potential delays (over straight QMTP); the
initial connection response by the foreign MTA, and the delay of waiting
for the EHLO round-trip.
As with RFC 1869 (introducing ESMTP) though, one of these could be
eliminated by simply changing "EHLO" to "QHLO" leaving us with a 500
response if the remote MTA does not understand QMTP. This adds a
round-trip every time we communicate with a non-QMTP MX, but that might
not concern many people. 'QMTP' could of course also be added to the
initial connection string to reduce things further.
Option #2:
< 220 IP ESMTP
> QHLO
< 2000 QMTP ready
> (data stream)
< (response)
Option #3:
< 220 IP ESMTP QMTP
> QHLO
> (data stream)
< (response)
I see this last one as being best, since the opening message can be
customised to mention QMTP in it easily, and once that is parsed by the
sending MTA, no further foreign responses are required until the QMTP
dialog is finished. The initial "QHLO" would be added to inform the
foreign MTA of our intentions.
Comments?
