Re: [exim] Shared Hosting + Specific Domain outbound filter

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Author: Heiko Schlittermann
Date:  
To: exim-users
Subject: Re: [exim] Shared Hosting + Specific Domain outbound filter
Rafael Wolf via Exim-users <exim-users@???> (Mo 29 Apr 2019 19:26:59 CEST):
> Hi All,
> from all domains.
>
> Example:
>
> *@customer.com > Subject: encrypt > forward to the Cuda smart host
> that will handle encryption based on subject
>
> *@customer.com > Subject: anything else here > goes out the door from
> the CPanel server
>
> I'm not quite sure after looking at forums, etc how to do this. I
> know I need to use a "router" function but how to lock it down to
> individual domain names for outbound filtering I'm just not certain
> and I can't figure out what I should do or where.


In Exim routers use the destination address for their routing decision
(as Layer 3 does). They can be forced to route based on other
information (e.g. the sender's domain). But the cleaner way is to have
another layer of decisions: pre-conditions. Exim router pre-conditions
help selecting the right router (comparable with ip rules in Linux).

A well known pre-condition is "domains", as used in most setups.
But there are more. For your issue I'd use the "senders" pre-condition
and the generic "condition" pre-condition:

A rough outline, w/o any tests applied, so it is up to you, to check if
this would work for you.


begin routers

    encrypt:
        # pre-conditions
        senders = *@customer.com
        condition = ${if match{$h_subject:}{^encrypt}}
        # if the pre-conditions are met:
        driver = manualroute
        route_data = <the smart host of your encryption provider>
        transport = smtp


    <and now all your other routers>


I reordered the configuration lines slightly, to point out the "pre".

Ah, beware: If your ACL do a routing check (as normally the RCPT ACL
does), *this* router won't be used, as during the RCPT ACL phase the
subject is not yet known.

    Best regards from Dresden/Germany
    Viele Grüße aus Dresden
    Heiko Schlittermann
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