I have Sieve set up for my system, and use the duplicate filter as follows:
# rule:[Duplicates]
if duplicate :header "message-id"
{
discard;
}
That's basically straight out of the RFC. (Along with the requisite 'require' of course.)
Other Sieve managers don't have a problem with that filter, but Roundcube not only doesn't "see" it when I load the filters to edit, but when I exit the Roundcube editor it saves my file without the duplicate filter. I have to re-add it by hand.
Thoughts?
In any case, thanks to the developers and contributors of this great system.