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Re: ml.org's dynamic DNS

On Tue, Mar 03, 1998 at 06:01:29AM -0000, bruce@va.debian.org wrote:

> >  - dyn.ml.org is a flat name space.  It's not hierarchical.  If too many
> >    users start trying to get these addresses, the entire structure will
> >    collapse.  Their approach not a good technical solution to the
> >    problem.
> Want to bring this up and see what they say? From my experience with
> ampr.org, BIND will handle 50,000 entries on what is now a modest system.
> Perhaps they are waiting for enough users to make more engineering
> necessary.

I'll contact them if there is interest.  (Thought I would volunteer first
because it would be embarrassing to have two Debian people talk to them :))

> >  - It doesn't solve all the problems.  The bugs are in the applications_,
> >    not the lack of a domain name.  Almost all ISP's provide you with a
> >    proper (though varying and not-so-pretty) domain name anyway -- it's
> >    just
> Can you solve the problem of keeping the envelope-from of your SMTP server
> the same over time without dynamic DNS? I could not think of how to do
> this. It sounds to me as if some other system might get my mail bounces.

I use a smarthost.  Given the choice, I like this approach better since it
allows a system with "real" net access to handle multi-recipient messages
and retries.

SMTP servers should not be validating the envelope-from (if by that, you
mean the MAIL FROM command in SMTP).  That would seriously confuse a lot of
things.  As a total.net user, I should be able to (and I can) send mail as
if I were apenwarr@bond.net, apenwarr@worldvisions.ca, apenwarr@debian.org,
and avery.pennarun@uwaterloo.ca.  I am all four.

The envelope-from should always be the same as the From: line, in my
opinion, unless you're sending spam or have some other special needs. 
Please let me know if this isn't what's happening in general.

My understanding of all this new (and important, but frustrating) SMTP
anti-forwarding stuff is that modern sites will do the following:

 - forward any mail from any host (as validated by the DNS, not the
   MAIL FROM or HELO) to anyone on the "local" network.
 - forward any mail from anyone on the "local" network to anyone on any

 - refuse to forward mail from anyone one outside the "local" network to
   someone else outside the "local" network.
Again, all hosts are validated by simply looking up the source IP address in
the DNS and searching for it in a table.  This should work fine, and prevent
people from using your site as a spam forwarder without being unnecessarily
annoying to real users.

In my opinion you should always HELO with a DNS-reversal of your IP address
-- whatever it may be.  (smail uses gethostbyname(), I think.) Then you MAIL
FROM with your _desired_ From: address -- the one you want your mail bounces
sent to.  If MAIL FROM does not match the From: header, the MTA should add
the Envelope-From: header.

Avery's idea of a perfect SMTP session

	HELO ppp-annex-0117.mtl.accent.net
	250 mail.spitball.com Hello ppp-anne.. [], nice
		weather we're having
	MAIL FROM: <apenwarr@worldvisions.ca>
	RCPT TO: <someone@spitball.com>
	From: apenwarr@worldvisions.ca
	To: someone@spitball.com
	Subject: Your ISP's name
	Where did your ISP get such a silly name, anyway?

Naturally this leaves out some of the more mundane SMTP responses and
ignores cc: and bcc: but you get the picture :)

I do almost this (I think my HELO line is wrong) and any bounces are
appropriately filed at apenwarr@worldvisions.ca, to be retrieved the next
time I do a POP request.  The last thing I want is for my bounces to bounce
-- they should be delivered to me reliably, just like all my mail.

Have fun,


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