Global duplicate filtering via Sieve

[Hanno Stock]

Hi everybody,

I have the following problem:

Our mail users are receiving mails from externally defined mail
forwardings and lists which sometimes leads to duplicate messages. As
far as I understand, a single user can use the Sieve duplicate extension
for filtering out such duplicate messages.

Would it be feasible to add a script with sieve_before that does this
for all users?

Do scripts that run from sieve_before store persistent data also on a
per-user basis, i.e. in the user's home dir?

Thanks for your help!

Best regards

Hanno