Re: [ietf-smtp] DSNs

Sam Varshavchik <mrsam@courier-mta.com> Tue, 28 April 2020 22:50 UTC

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From: Sam Varshavchik <mrsam@courier-mta.com>
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Date: Tue, 28 Apr 2020 18:50:45 -0400
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Subject: Re: [ietf-smtp] DSNs
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John Levine writes:

> In article <cone.1588076349.709902.75652.1004@monster.email-scan.com> you  
> write:
> >> In general I agree but there are still situations where an MTA (mine
> >> for example) accepts a message intending to forward it somewhere else
> >> and then the forward fails.  Either send a DSN or drop it on the floor
> >> at that point.
> >
> >Well, yes. You take ownership of that message by the act of forwarding, you
> >now own it, from the point of forwarding. If you don't want to disclose the
> >forwarded-to address, that's your responsibility, so either set the sender's
> >address to <>, or to some other address where you want the bounces to go.
>
> Huh?  If I send a DSN it includes the original delivery address but it
> doesn't have to include the forwarded-to address.

I'm talking about the forwarding system. Whatever's forwarding the message,  
it can easily reset the return address to <>, or to some bit bucket.

>From that point on, any DSN can be sent normally. It won't go anywhere, and  
the sender will never see it.

For all practical matters, the forwarding system is the end recipient, and  
would report any success DSN. Hooray, your message was received by  
mrsam@courier-mta.com.

The fact that it gets forwarded to sam.varshavchik@gmail.com by my  
forwarding script (it's not, this is just as an example) is something that  
you have any knowledge of. The return address on the forwarded message is  
not johnl@taugh.com any more, it's nobody@courier-mta.com. Or maybe it's  
even <>. You have no knowledge of that, either. Since I received the mail,  
and I decided to forward it, I can change the return address. There is no  
law that says that I must keep it the same.

Either way, since I set up the forwarding: if it breaks and I lose my mail,  
I only have myself to blame and noone else. Noone else is responsible for my  
forwarded mail other than myself.

But, as far as you're concerned, you sent mail to mrsam@courier-mta.com with  
NOTIFY=SUCCESS, and you got a DSN stating that fact. That's all you know.  
Did I get it at this address, or the other one? You'll never know.