[exim] autoreply if mail not delivered (filter)

Hi all,

I´m using exim4 with exim.filter-file.
With this filter I check different header_subjects, reply_addresses and Header Flags and then decide to move the mails to spam-folder or not.

For incoming mails this is ok, but the question is, how can I implement an autoreply only for internal senders, if a message get fetched by the filter and so not delivered/moved to spam?

Is this best done via filter-file or by exim.conf?

any help would be welcome, thx