Re: Setting Reply-To: using exim?
Thanks for your reply on this. There are still some things I don't
understand very well though.
brian moore [bem@cmc.net] wrote:
> On Wed, Feb 07, 2001 at 10:05:13AM +1030, Mark Phillips wrote:
> > Sean 'Shaleh' Perry [shaleh@valinux.com] wrote:
> > > enable /etc/email-address use. I use this so that mail from
> > > shaleh@mymachine.whereiam.foo becomes shaleh@whatIwant.com.
> >
> > I could do this, but I have been told in the past that this is bad.
> > Let me explain what I was told. If my secondary isp thinks of me as
> > "markphillips@cheapisp.com.au", but the email address I want to use is
> > "mark@infoeng.flinders.edu.au" then as you say I could rewrite
> > addresses so that markphillips@cheapisp.com.au becomes
> > mark@infoeng.flinders.edu.au. But then my machine is lying. It
> > pretends to be sending from infoeng.flinders.edu.au when really it is
> > sending from cheapisp.com.au. Apparently the smtp transaction envelop
> > will still show the email as originating from cheapisp.com.au. And
> > apparently some mailservers don't like this discrepancy. If the
> > envelope sender is different from the headers sender then it rejects
> > the email, causing it to bounce. And this bouncing has even more
> > problems. It bounces it back to the envelope sender domain. So
> > cheapist.com.au gets the bounced message, but they don't know what to
> > do with it, because the "From:" address is one they don't recognise.
>
> Any mail server that did that would be severly broken. Errors have gone
> to the SMTP envelope sender for 20 some years.
Yes it does use SMTP envelope sender, but the problem (I was told) was
that when the bounced message got back to cheapisp.com.au they didn't
know what to do with it. Presumably the SMTP envelope sender
information didn't include the username "markphillips", but rather,
the username "mark" which cheapisp.com.au has no knowledge about. I
think this was the problem anyway.
I must confess that I'm a little confused about SMTP envelopes. I
don't know where the SMTP envelope information is stored or exactly
what information is stored. Does it keep a log of all the past SMTP
transactions in the history of the message? Can I go somewhere on my
machine and look at it? How does envelope information differ from
header information?
> Any mail server that compares SMTP envelopes with the domain of prior
> mail servers is -broken-.
>
> Any mail server that compares the SMTP envelopes with the 'body From:'
> is broken. (See this very item: where the SMTP envelope will say
> debian.org and yet I have no address on any debian server.)
>
> Masquerading has been common for 20 years. If people are attempting
> to detect it in some misguided effort to eliminate spam, they will lose
> a lot of mail.
When this problem arose, part of the problem I think, was that the
SMTP sender was mark@localdomain.org.au or something, ie the domain
"localdomain.org.au" didn't even exist. I could have fixed it to
"infoeng.flinders.edu.au", but from what this guy was telling me, even
this wasn't good enough. He said some mail servers nowdays were
starting to reject emails where there was a domain mismatch between
where the email orginated from and where it said it originated from.
I think he was saying that if you set things up this way, the fact is
that some email is going to bounce. I'm still a little confused
though about exactly how this works. Ie, I'm not sure it was the
"From:" address that was being looked at or not. Could a mail server
compare the envelope sender address with the email's mail server
history to see if the two matched or something? I'm still not sure
exactly how all this works.
The other point is: if rewriting addresses in this way is completely
legitimate, what point is the "Reply-To:" field?
Thanks,
Mark.
--
_/~~~~~~~~\___/~~~~~~\____________________________________________________
____/~~\_____/~~\__/~~\__________________________Mark_Phillips____________
____/~~\_____/~~\________________________________mark@ist.flinders.edu.au_
____/~~\HE___/~~\__/~~\APTAIN_____________________________________________
____/~~\______/~~~~~~\____________________________________________________
__________________________________________________________________________
"They told me I was gullible ... and I believed them!"
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