Mailing List Archive

Bounce Back Envelope From
Hi All,

All bounce-backs have an envelope from of <>.

I need to be able to set this to something. I am using a smart host that will not accept emails from <>. I need to to be set to postmaster or don-no-reply or something of the like.

Thanks for any help!
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Re: Bounce Back Envelope From [ In reply to ]
On 06/29/2018 08:30 PM, David Cunningham via Exim-users wrote:
> All bounce-backs have an envelope from of <>.
>
> I need to be able to set this to something. I am using a smart host that will not accept emails from <>. I need to to be set to postmaster or don-no-reply or something of the like.

That would be a very bad move, with the potential of bounce loops.
That is why the envelope from for a bounce is empty. Standards
mandate it.

You need to discuss the situation with your smarthost.
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Jeremy


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Re: Bounce Back Envelope From [ In reply to ]
> On Jun 30, 2018, at 9:04 AM, Jeremy Harris via Exim-users <exim-users@exim.org> wrote:
>
> On 06/29/2018 08:30 PM, David Cunningham via Exim-users wrote:
>> All bounce-backs have an envelope from of <>.
>>
>> I need to be able to set this to something. I am using a smart host that will not accept emails from <>. I need to to be set to postmaster or don-no-reply or something of the like.
>
> That would be a very bad move, with the potential of bounce loops.
> That is why the envelope from for a bounce is empty. Standards
> mandate it.
>
> You need to discuss the situation with your smarthost.
> --
> Jeremy
>
>
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Hi All,

I recognize that this is a bad idea, and it would be only temporary. I just need to find a way to do it for now so my undeliverable messages get delivered while I slap that smart host around.

Dave
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Re: Bounce Back Envelope From [ In reply to ]
On 29 Jun 2018, at 15:30, David Cunningham via Exim-users wrote:

> Hi All,
>
> All bounce-backs have an envelope from of <>.

Yes, they do. Using the null sender for MTA-generated messages has been
part of the SMTP standard forever. It is not optional. It is not a
matter of choice. A server which does otherwise is a broken server and a
public nuisance. A purported "bounce" message with a non-null envelope
sender SHOULD NOT be delivered and MAY be considered prima facie
evidence of the originating machine being under the control of a
malicious actor, because this behavior has been exhibited by
(desperately stupid) spambots.

> I need to be able to set this to something.

That is not true. You will survive conforming to the standard. Using a
non-null sender on bounces is bad and wrong and no one should ever do it
for any reason. It is better that you simply blackhole all of your
bounces rather than send broken ones.

> I am using a smart host that will not accept emails from <>.

Are you convinced that "smart" is the right word here? I'm quite certain
it is not. Maybe you meant "grossly misconfigured outbound relay"
instead?

> I need to to be set to postmaster or don-no-reply or something of the
> like.

The consequences of doing so will be remote double-bounces aimed at the
envelope address (which had best accept all mail, or you're running an
echo chamber,) your bounces going missing silently, possible public
blacklisting, and almost certain private undiagnosable blacklisting.
These annoying consequences will be entirely deserved.

With that said, a conditional string expansion in the return_path option
of the smtp transport would be the way to do this. See the docs:
http://www.exim.org/exim-html-current/doc/html/spec_html/ch-generic_options_for_transports.html
http://www.exim.org/exim-html-current/doc/html/spec_html/ch-string_expansions.html

Something *like* (untested):

return_path = ${if eq {$return_path}{} {postmaster@example.com}}

But in case I wasn't clear: DO NOT DO THIS!

(yeah, I know, you won't listen...)


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Bill Cole
bill@scconsult.com or billcole@apache.org
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Currently Seeking Steadier Work: https://linkedin.com/in/billcole

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Re: Bounce Back Envelope From [ In reply to ]
On Mon, Jul 2, 2018 at 6:40 PM, Bill Cole via Exim-users <
exim-users@exim.org> wrote:

> On 29 Jun 2018, at 15:30, David Cunningham via Exim-users wrote:
>
>
>> I am using a smart host that will not accept emails from <>.
>>
>
> Are you convinced that "smart" is the right word here? I'm quite certain
> it is not. Maybe you meant "grossly misconfigured outbound relay" instead?


I think another issue to keep in mind is that certain broken e-mail clients
also send messages with the empty envelope sender in response to spam. "I'm
on vacation", "This message has been read", "This message has been deleted".

Maybe the "smarthost" is for end-user e-mail clients, and not for servers,
and therefore has stricter rules in order to avoid these issues?

--
Jan
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Re: Bounce Back Envelope From [ In reply to ]
On Tue, Jul 03, 2018 at 06:46:25AM +0200, Jan Ingvoldstad via Exim-users wrote:
> On Mon, Jul 2, 2018 at 6:40 PM, Bill Cole via Exim-users <
> exim-users@exim.org> wrote:
>
> > On 29 Jun 2018, at 15:30, David Cunningham via Exim-users wrote:
> >
> >
> >> I am using a smart host that will not accept emails from <>.
> >>
> >
> > Are you convinced that "smart" is the right word here? I'm quite certain
> > it is not. Maybe you meant "grossly misconfigured outbound relay" instead?
>
>
> I think another issue to keep in mind is that certain broken e-mail clients
> also send messages with the empty envelope sender in response to spam. "I'm
> on vacation", "This message has been read", "This message has been deleted".

The 2nd and 3d messages may be treated as Message Disposition Notifications
(MDNs), and 1st message may be admittedly assigned to this cathegory too.
All MDNs must be sent from <> address, as RFC3798 says in p.3:

The envelope sender address (i.e., SMTP MAIL FROM) of the MDN MUST be
null (<>), specifying that no Delivery Status Notification messages
or other messages indicating successful or unsuccessful delivery are
to be sent in response to an MDN.

The most impotant reason to treat mentioned messages as MDNs, I think, is
the fact they SHOULD NOT be answered. If such message has user's envelope
address, autoreply or other MDN may be generated, forming mail loop.

So, broken e-mail clients are those that put user's address to envelope
sender for MDNs, particularly Outlook and MS Exchange.
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Eugene Berdnikov

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Re: Bounce Back Envelope From [ In reply to ]
On Wed, Jul 4, 2018 at 9:51 AM, Evgeniy Berdnikov via Exim-users <
exim-users@exim.org> wrote:

> On Tue, Jul 03, 2018 at 06:46:25AM +0200, Jan Ingvoldstad via Exim-users
> wrote:
> > On Mon, Jul 2, 2018 at 6:40 PM, Bill Cole via Exim-users <
> > exim-users@exim.org> wrote:
> >
> > > On 29 Jun 2018, at 15:30, David Cunningham via Exim-users wrote:
> > >
> > >
> > >> I am using a smart host that will not accept emails from <>.
> > >>
> > >
> > > Are you convinced that "smart" is the right word here? I'm quite
> certain
> > > it is not. Maybe you meant "grossly misconfigured outbound relay"
> instead?
> >
> >
> > I think another issue to keep in mind is that certain broken e-mail
> clients
> > also send messages with the empty envelope sender in response to spam.
> "I'm
> > on vacation", "This message has been read", "This message has been
> deleted".
>
> The 2nd and 3d messages may be treated as Message Disposition
> Notifications
> (MDNs), and 1st message may be admittedly assigned to this cathegory too.
> All MDNs must be sent from <> address, as RFC3798 says in p.3:
>
> The envelope sender address (i.e., SMTP MAIL FROM) of the MDN MUST be
> null (<>), specifying that no Delivery Status Notification messages
> or other messages indicating successful or unsuccessful delivery are
> to be sent in response to an MDN.
>
> The most impotant reason to treat mentioned messages as MDNs, I think, is
> the fact they SHOULD NOT be answered. If such message has user's envelope
> address, autoreply or other MDN may be generated, forming mail loop.
>
> So, broken e-mail clients are those that put user's address to envelope
> sender for MDNs, particularly Outlook and MS Exchange.
>

No, Outlook does not do this. Outlook is one of those who, brokenly, send
MDNs, generating backscatter.

Maybe MS Exchange can be configured to generate backscatter similarly, I
don't know.

--
Jan
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Re: Bounce Back Envelope From [ In reply to ]
On Wed, 4 Jul 2018, Jan Ingvoldstad via Exim-users wrote:

> On Wed, Jul 4, 2018 at 9:51 AM, Evgeniy Berdnikov via Exim-users <
> exim-users@exim.org> wrote:
>
> > > I think another issue to keep in mind is that certain broken e-mail
> > clients
> > > also send messages with the empty envelope sender in response to spam.
> > "I'm
> > > on vacation", "This message has been read", "This message has been
> > deleted".
> >
> > The 2nd and 3d messages may be treated as Message Disposition
> > Notifications
> > (MDNs), and 1st message may be admittedly assigned to this cathegory too.
> > All MDNs must be sent from <> address, as RFC3798 says in p.3:
> >
> > The envelope sender address (i.e., SMTP MAIL FROM) of the MDN MUST be
> > null (<>), specifying that no Delivery Status Notification messages
> > or other messages indicating successful or unsuccessful delivery are
> > to be sent in response to an MDN.
> >
> > The most impotant reason to treat mentioned messages as MDNs, I think, is
> > the fact they SHOULD NOT be answered. If such message has user's envelope
> > address, autoreply or other MDN may be generated, forming mail loop.
> >
> > So, broken e-mail clients are those that put user's address to envelope
> > sender for MDNs, particularly Outlook and MS Exchange.
> >
>
> No, Outlook does not do this. Outlook is one of those who, brokenly, send
> MDNs, generating backscatter.
>
> Maybe MS Exchange can be configured to generate backscatter similarly, I
> don't know.

Slightly diverging into the issue of autoreplies;

Don't forget that some systems take regard of other headers in deciding
whether or not to autoreply, which can mitigate some of the potential
backscatter, particularly the RFC3834 Auto-Submitted header and the
Precedence header.

Exchange also has X-Auto-Response-Suppress which another Exchange system,
or something else that has been programmed to pay attention to that
header, can also heed.

I wrote the bulk of this page many years ago on the general topic of
autoreplies: https://github.com/Exim/exim/wiki/EximAutoReply

If I have control of it, for transactional email, I add something like:

Auto-submitted: auto-generated
X-Auto-Response-Suppress: OOF
Precedence: junk

whether or not it is null sender.

I even look at inbound mail to my site, and if by various criteria I
determine that it shouldn't have an auto-reply sent to it, then I will add

X-Auto-Response-Suppress: OOF, DR, RN, NRN

to the message to discourage our internal Exchange system from generating
an autoreply. Criteria are the presence/content of certain headers (list
auto-submitted and precendence), certain sender address patterns (things
that look like lists, info@, donotreply@ etc) and also certain recipients.

It's all kind of a mess, but lots of the little solutions help the overall
problem.

Jethro.

. . . . . . . . . . . . . . . . . . . . . . . . .
Jethro R Binks, Network Manager,
Information Services Directorate, University Of Strathclyde, Glasgow, UK

The University of Strathclyde is a charitable body, registered in
Scotland, number SC015263.

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