Mailing List Archive

Question about SRS
Hi list,

after studying the documentation about SRS
(https://www.exim.org/exim-html-current/doc/html/spec_html/ch-dkim_spf_srs_and_dmarc.html#SECTSRS)
I have a problem understanding one detail:

Why is it required to set max_rcpt=1 in the remote_forwarded_smtp transport?

The documentation seems not to include any reasons, why you have to do
this for SRS forwards (explicitly).

I even found an example where this might be disturbing: Imagine a mail
alias based list with n recipients at the same external destination
domain (e.g. some freemailer). If some x recipients of them have e.g.
quota issues, the original sender will get x bounce messages. With
max_rcpt=100 (the default), the sender will get only one bounce with a
list of x failed recipients. This example is independent of SRS, however
if SRS is in use, the local MTA also has to deal with x bounces to be
forwarded back to the original sender.

Regards,
--
Patrick Cernko <pcernko@mpi-klsb.mpg.de> +49 681 9325 5815
Joint Scientific IT and Technical Service
Max-Planck-Institute für Informatik & Softwaresysteme
Re: Question about SRS [ In reply to ]
On 03/03/2023 13:22, Patrick Cernko via Exim-users wrote:
> Why is it required to set max_rcpt=1 in the remote_forwarded_smtp transport?

For $original_domain to be valid. If the transport was handling multiple
recipients then the domains could potentially be disparate.
--
Cheers,
Jeremy


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Re: Question about SRS [ In reply to ]
Hi Jeremy,

On 03.03.23 15:05, Jeremy Harris via Exim-users wrote:
> On 03/03/2023 13:22, Patrick Cernko via Exim-users wrote:
>> Why is it required to set max_rcpt=1 in the remote_forwarded_smtp transport?
>
> For $original_domain to be valid.  If the transport was handling multiple
> recipients then the domains could potentially be disparate.

thanks for the quick response!

So if I do not use $original_domain but some fixed domain like
$qualify_domain or "srs.mydomain.org", I can skip setting max_rcpt=1?
(obviously I have to use that domain in the inbound_srs* routers then)

Best regards,
--
Patrick Cernko <pcernko@mpi-klsb.mpg.de> +49 681 9325 5815
Joint Scientific IT and Technical Service
Max-Planck-Institute für Informatik & Softwaresysteme
Re: Question about SRS [ In reply to ]
On 03/03/2023 14:47, Patrick Cernko via Exim-users wrote:
> obviously I have to use that domain in the inbound_srs* routers then

Plus any other places where your config has a notino as to what
it does with what domain names. You're moving further away from a
basic set; you'll need to reason about it yourself.
--
Cheers,
Jeremy


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