RE: Resume command for ESMTP?

[Gaurang Pandya <gaubrig at yahoo.com>]

Hi Frank,

I liked all these ideas very much.
But I may be of no use to you since i am newbie.

Gaurang.
--- Franck Martin <Franck at sopac.org> wrote:
> Vladis,
> 
> You won't get me I though about this one ;-)
> 
> As I said in my previous e-mail there are several
> cases to handle error and
> security related to such command...
> 
> First of all I feel it is important to implement
> such mechanism to avoid to
> increase the digital divide between countries which
> have bandwidth and
> countries which have not. I see so many sites which
> disregard servers
> because the latency is too big or the downloads are
> too slow. Basically they
> send the message: we don't want to talk with you
> because you are inferior. I
> won't give names but they exist and are not the
> small companies...
> 
> Basically, I would like your cooperation in trying
> to make this thing work.
> If you think there is an issue try to imagine the
> RESUME command exists and
> how it should respond to the problem...
> 
> Enough rant, let's go back to technical issues.
> 
> The mail server needs obviously to become more
> intelligent, than store,
> forward and forget.
> 
> First to put the RESUME command just before DATA
> ensure that most of the
> sanity checks have been passed (RBL, fake domain,
> ESMTP size too big,...).
> So, so far nothing really has happened...
> 
> Now let see how someone could do a DOS and how the
> server should avoid it.
> 
> The first principle, is not to store a mail part
> indifinitively, but to
> timeout it in the queue. The parameter should be
> left configurable. Let's
> say that the mail sender has 5mn to resume the
> session or it has to start
> from the beginning again. This would allow that the
> queue doesn't grow out
> of proportion because of errors.
> 
> The second principle, is that most servers do a
> content analysis based on
> the line received. The mail server, needs to know
> where it is in the
> session. Are we still in the headers or already in
> the content? Based on
> content anylysis of the mail being received the
> server may send an error
> back, like "Error content rejected", "Malformed
> error", "Message to big".
> The server trash the message and clear the session.
> This would take care of
> the sircam virus, like on my system where I block
> attachments with .exe or
> .lnk extensions. This is done easily on the fly
> while receiving the e-mails.
> Here the e-mail does not need to be fully received
> but as soon as a
> condition is met the session is closed.
> 
> The thrid issue, is that some mail system, get the
> whole e-mail then pass it
> to an antivirus software before re-injecting the
> e-mail back into the
> system. There is no possibility than to wait the
> completion of the whole
> session, but with the timeout above, you can't keep
> a session open too
> long...
> 
> Finally, there could be a separate resume queue with
> a fixed size limit so
> that after receiving the RESUME command the server
> may answer "NOT AVAILABLE
> NOW". It is then up to the sender to try to send or
> try later. Later the
> messages queued will expire and the RESUME queue
> will be available again...
> 
> The RESUME capability is useful only for big mail in
> poor network
> conditions. The SIZE limit is for queue space and
> processing capabilities,
> it should'nt be used as a poor network configuration
> parameter...
> 
> I understand that a mail server with RESUME
> capability may need a bigger
> queue than one without, but HD space is cheap, and
> it saves huge amount of
> expensive bandwidth...
> 
> So What do you think? Anybody that support the idea
> and want to develop it
> further?
> 
> Franck Martin
> Network and Database Development Officer
> SOPAC South Pacific Applied Geoscience Commission
> Fiji
> E-mail: franck at sopac.org <mailto:franck at sopac.org> 
> Web site: http://www.sopac.org/
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> This e-mail is intended for its addresses only. Do
> not forward this e-mail
> without approval. The views expressed in this e-mail
> may not be necessarily
> the views of SOPAC.
> 
> 
> 
> -----Original Message-----
> From: Valdis.Kletnieks at vt.edu
> [mailto:Valdis.Kletnieks at vt.edu]
> Sent: Monday, 6 August 2001 7:45 
> To: Franck Martin
> Cc: ietf at ietf.org
> Subject: Re: Resume command for ESMTP? 
> 
> 
> On Sun, 05 Aug 2001 19:39:21 +1200, Franck Martin
> <franck at sopac.org>  said:
> 
> 
> > So ESMTP could have an extension called RESUME
> > 
> > The protocol would be standard, except that before
> DATA and after RCPT
> > TO, the sending server who has identified the
> RESUME keyword could ask a
> > RESUME session...
> 
> On the other hand, SMTP is a store-and-forward
> system where the files are
> kept in essentially *temporary* storage.  As such,
> the general design
> philosophy is to throw away the temporary files if a
> transfer fails, so
> as to free up queue space.
> 
> This in and of itself is not a problem, until you
> realize that quite
> possibly
> more than one file may need to be saved in case the
> person will *someday*
> try to RESUME the transfer.  Now.. a real-life case
> in point.
> 
> And that's why there isn't a RESUME.
> 
> -- 
> 				Valdis Kletnieks
> 				Operating Systems Analyst
> 				Virginia Tech
> 


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