Hello,
>>We also handle email-forwardings and rewriting and adding headers shall
>>only be done on incoming mail.
>
>
> try adding:
>
> headers_add = ${if your_condition {Subject: *SPAM* $h_subject}{}}
> headers_remove = ${if your_condition {Subject}{}}
>
> to your local delivery router, in which the header should be rewritten.
thanks, that was what I was looking for! I just forgot that headers_add
exists although I used it before in another exim setup.
I'm not 100% happy with this solution as now every email runs through
the spam filter and increases CPU load although maybe no action is taken
after the check, but I guess there is no other way.