[Dovecot] trash plugin together with sieve_before ?

We have a sieve script doing sieve_before to sort spam to spam-folders. Now I'm trying to configure the "Trash" plugin, but it doesn't seem to work.. I noticed my config file says:

# Space separated list of plugins to load (none known to be useful so far). Do NOT # try to load IMAP plugins here. #mail_plugins =

and that doveconf doesn't list any plugins loaded for "protocol sieve". Should we load quota and trash here ?

-jf