Subject: Re: Mail-Transmitter RR

From: Derek Atkins <[email-masked]>
Date: 01 Jun 2002 22:40:29 -0400

Ted Lemon <[email-masked]> writes:

> > Agreed.  I send mail from my laptop, which travels with me all over
> > the place, but my From address is elsewhere.  How is my home address
> > supposed to know what IP address I'm using at any particular point in
> > time?
> 
> You contact an SMTP server for your domain over SSL, authenticate yourself,
>   and drop the main on that server, which can then safely forward it.

Who is "you" in this case?  My MUA?  My MTA?  I'm currently running
sendmail on my laptop.  My MUA just passes the mail on to there, and
it gets forwarded appropriately.  This is a nice feature because there
are many times when I have better connectivity between my laptop and
my recipient than I would going from laptop->home->recipient.  Are you
saying that instead of distributing the load of mail I now have to
centralize mail delivery just because people are abusing the
distributed nature?

> So don't use MAIL-FROM if it doesn't work for you.   I think this is
> an unlikely problem, though.   I use a remote mail drop for every
> email message I send, and it has never caused me any inconvenience.

Perhaps your definition of inconvenience and mine are different?  But
consider this: if not everyone is doing it, then what's the point?  If
it's not a ubiquitous solution, then it's not going to solve the spam
problem.  All it will do is prevent spammers from forging a valid
email address to recipients that have agreements with that individual.

I was hit by this today... Some spammer used my address to send out a
bunch of messages, and I was lucky enough to get all the bounces into
my inbox.  I certainly did not know any of the recipients whose mail
bounced back to me.  So, how would this have helped me (or them) in
this case, especially if you're telling me not to use it?

> This proposal doesn't solve the spam problem, but it _does_ make it
> harder for spammers to get away with forging email addresses, which
> would be a big improvement.   What's more, it does not require that
> you agree to it.   It only requires that people who are victims of
> forgery agree to it, and that people who care about forgery agree to
> it.   So if you don't like it, don'
> t do it.

See, I'm not convinced it will make it much more difficult unless it's
a upqiwuitous deployment, and I believe that the functionality that is
destroyed by deploying this technology is not worth the perceived
benefit.

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
       [email-masked]                        PGP key available

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---

From: "Eric A. Hall" <[email-masked]>
Date: Sat, 01 Jun 2002 22:42:39 -0500

> email address to recipients that have agreements with that individual.

This is the crux of *an* argument, but not *the* argument, IMO.

 Negative: The spammers will stop using hotmail.com, will scurry
    away from the bright light, and will start forging mail from
    somebody else's domain. Zero-sum gain for us, the recipients
    of spam.

 Negative: We lose a valuable filter (DENY HOTMAIL.COM).

 Positive: Hotmail has control over it's domain. I can accept
    mail from them again.

 Positive: Nobody will send forgeries from *my* domain. They
    will not announce winners for contests I've never held. They
    will not spread trojans *from other networks* claiming to be
    coming from me.

 Positive: Nobody will send forgeries from *your* domain, if you
    choose to opt-in to the self-ACL scheme.

 Positive: I have another weighting filter for my post-transfer
    filtering scheme, whereby non-participants are slightly less
    credible, while participants get whitelisted automatically.

There is only one negative that hurts. The other negative is a neutral.

There are certainly other valid issues with this approach. It can be very
difficult for ultra-mobile users to participate, for example. But it is
also elective, and only applies to the mail domain under your control.

I just can't see anything wrong with letting people say "only accept mail
from me if it comes from this network".

-- 
Eric A. Hall                                        http://www.ehsco.com/
Internet Core Protocols          http://www.oreilly.com/catalog/coreprot/

---

From: Mathias Koerber <[email-masked]>
Date: Sun, 02 Jun 2002 12:11:05 +0800

> centralize mail delivery just because people are abusing the

I wouldn;t say 'have to'. If you have other ,ethods of authenticating your
mail (ie pgp etc), the receiving MTAs should be free to ignore the
MAIL-FROM RR if they can authenticate you that way.

The problem with that approach is that they would have to receive the
complete email first, *and* that they'd need the ability to do 
authentication
which usually now is done in the MUA.
On the otherhand, this approach is *voluntary*, and no-one forces you to
publish your MAIL-FROM MX ifyoudon't want to use it.

> email address to recipients that have agreements with that individual.

No. The beuaty of thes approach is that there is no specific agreement
between each pair of potential senders and recipients necessary.
A recipeint decides whether s/he wants to use this method of MAIL-FROM
is such an RR exists for the sender, and the sender simply published
it if they want their addresses protected from abuse (at least to those
sides that actually check for it).

> this case, especially if you're telling me not to use it?

You can't have it both ways. It will help you only if you use it, but
that means using list of predefined MX hosts. There are tradeoffs.
If you really want, you can list your laptop in the MAIL-FROM MX
list and use DDNS to update its IP address before sending mail.
There should not be any problems with the mail hanging around and
someone checking the MX after you lose that IP address, as it is the first
MTA after your sender that will have to perform this check.

> destroyed by deploying this technology is not worth the perceived

I don's see any functionality being destroyed. You will have to make a 
choice
which is more important to you, fast, shortest-hop delivery to the nearest
recipient MTAs or the protection of your address(es).

mk

---

From: "Andy W. Barclay" <[email-masked]>
Date: Sun, 02 Jun 2002 05:04:24 -0700

Hi Derek,
Actually, I do advocate that you send all mail from your laptop
through your home machine, then on to the final recipient.

This is no different from the way 90% of the population of the Internet 
does things now. Most people don't run sendmail on their laptop.
In fact, I am currently connected to the net via a dsl connection
to sympatico in Canada right now. The sympatico firewalls block
out-bound SMTP, so you are supposed to use their SMTP servers. (I tunnel
smtp to my home server via ssh). This would adversely affect your 
ability to use your laptop as a relay. Lastly, the mail-abuse.com people 
define a method of blocking mail which comes from "dial-up" addresses.

I think that your solution of using your laptop will slowly become
less and less reliable, and I think that both Paul's proposal and
David Green's proposal have merit. (In case anyone is interested,
several of my compatriots are using spamassassin to kill spam,
and its working very well for them (99.5% success rate, .4% false
positives)

-- 
Regards,
Andy W. Barclay.        [email-masked]
fax  (781) 823-8276
Always a UNIX Evangelist (and sometimes a system and network architect)

The truth of a proposition has nothing to do with its
credibility. And Vice-Versa.

---

From: Måns Nilsson <[email-masked]>
Date: Sun, 02 Jun 2002 18:38:29 +0200

--On Sunday, June 02, 2002 05:04:24 -0700 "Andy W. Barclay"
<[email-masked]> wrote:

> does things now. 

Perhaps 90% of the people on the Internet use Windows. Are you suggesting
we  should force everyone to use Windows just because 90% of the people on
the Internet do so? 

The proposal(s) break(s) e-mail in fundamental and worrying ways, and make
the probability of e-mail delivery in adverse conditions much lower (think
backhoe incident on main internet connectivity, trigging the use of dialup
for backup connectivity, and nobody remembering to add that netblock to the
good, allowed ones).

Us moderately and above clued people should not destroy the "survive-all"
capabilities of the Internet. There are others doing that much better. 

This is a bad suggestion, and it needs to be stopped. 

/Måns, who has a sendmail running on his laptop. 
-- 
Måns Nilsson            Systems Specialist
+46 70 681 7204         KTHNOC  MN1334-RIPE

We're sysadmins. To us, data is a protocol-overhead.

---

From: "Al Costanzo" <[email-masked]>
Date: Sun, 2 Jun 2002 12:36:11 -0400

Sorry,

IMHO it breaks nothing. It is not a required RR it is a suggested one. If
you cant SPAM in your mailbox fine, for those of us who do not it is an
excellent idea.

-al

---

From: David Green <[email-masked]>
Date: Sun, 2 Jun 2002 13:21:58 -0400 (EDT)

> for backup connectivity, and nobody remembering to add that netblock to the

My idea doesn't break or change anything. It just allows endpoint SMTP 
servers to add a header to mail, which may or may not be examined by 
end-user MUAs.

David Green

---

From: Randy Bush <[email-masked]>
Date: Sun, 02 Jun 2002 10:34:04 -0700

thanks, måns.  indeed, many of us don't run windoze and don't think
colonial mail routing.

the problem is that this is really a side-eddy to the spam maelstrom.
this discussion is about all sorts of hacks to allow one to force the
source of the mail to be honest about whence it comes.  while this is
nice, it is indirect and merely gives you a slight leg up on chasing
ten thousand slimeballs.  it is like trying to use source spoofing
prevention to stop ddos attacks, a useful tool but not a real solution
by a long shot.

so how much should we mangle the net (prevent direct delivery of mail
from laptops etc) for a partial approach to being able to assign
responsibility to spammers who will ignore responsibility anyway?

randy

---

From: "Eric A. Hall" <[email-masked]>
Date: Sun, 02 Jun 2002 13:04:32 -0500

> responsibility to spammers who will ignore responsibility anyway?

I would suggest that the mail network is already mangled. This is a way to
clean up my own little corner of the network with no impact to you. You
would be under no obligation to do this for your own network, or to query
my network. You can ignore it, just as you ignore any other scheme you do
not want to participate with.

The silver bullet exists, but in the form of a new message format and
transfer protocol. Goooood luck with that one.

Leathering through RBLs, reverse-path verification, keyword filters,
distributed checksums, are all things that people use now. An authorized
sender RR/owner/whatever is just another tool in the toolbelt. This one at
least has the interesting property that it is voluntary, meaning that when
it exists, it has more credibility than third-party mechanisms.