Sieve experts: How might I mark a copy I've made with fileinto :copy "Archive"; as read, but not the original?

@rjek I’ve been wondering this for *years*. Never found a way of making it work.

@jogbert For reference (it took me about 2 mins to work it out) set the seen flag, do the fileinto and then clear the flag before the keep.

@dsilverstone Care to gist it? I think I’m using the Dovecot sieve implementation and was never sure how complete it is.