How to remove duplicates in Exim .forward file?

Question

I would like to remove duplicates messages in some mailing-lists (cross-list posting) in my Exim .forward file.

I was using procmail before with these commands:

:0 Wh: msgid.lock
| /usr/bin/formail -D 8192 msgid.cache

What is the right way to achieve this using .forward Exim files?

Answer 1

This isn't really possible to do with Exim filter files. It might be possible to do with embedded Perl or abusing the database lookups, but this would require changing the system exim.conf.