[exim] seen condition

Hi all,

I can't seem to get the "seen" condition working. For testing purposes I copied the example in https://www.exim.org/exim-html-current/doc/html/spec_html/ch-access_control_lists.html

exim will not accept that and throws the error:
error in ACL: unknown ACL condition/modifier in "defer        seen    = -5m / key=${sender_host_address}_$local_part@$domain"

what am I missing?

Cheers
Hardy

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