SMTP "TURNME"

[Matti Aarnio <mea@nic.funet.fi>]

Hello,

	Due to some need, I decided to do an attempt at creating
	a safe way to enable user to initiate scheduling to any
	target system.

	The RFC-821 defines a "TURN" command, however:
	- it has not been defined adequately -- how it knows which
	  host is in the question ?  From HELO argument ?
	- it is widely considered a security hole - or very least
	  privacy invasion, and thus it has not been implemented
	  (One can rob email targeted to other systems with it.)
	

	As the scheduler attempts to send email out, it may get
	a (connection) timeout at some point, and thus be forced
	to retry, and the retries have backoff..

	Now enter a dialup user, who wants to minimize the time
	at the connection, and still get email via SMTP.  Thus
	this user needs a way to "kick" the scheduler to do an
	early retry, and not wait for 2-6 hours:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TURNME mea.cc.utu.fi
250-A TURNME request is initiated - lets hope the system
250-has resources to honour it.   We call the remote, if
250 we have anything to send there.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

	It does not interact with the scheduler to know, if this
	target system has anything in the queue; thus the "canned"
	message.

	The argument to  TURNME  is target system HOST string
	as used by the scheduler.  Especially it does NOT pay
	any attention to the CHANNEL specifier.  All threads
	with this HOST-string are kicked immediately.
	(Consider:  local/aabbcc  vs.  uucp/aabbcc)
	(It is used in case insensitive manner, though.)


	You can test the feel of it at  nic.funet.fi's SMTP-server,
	and get it at next source dump; somewhen..

/Matti Aarnio <mea@nic.funet.fi>