I use another method:
In the Admistration Console set tag and kill percent to the same value.
$sa_dsn_cutoff_level = 100;
$sa_quarantine_cutoff_level = 100;
$spam_quarantine_to = 'firstname.lastname@example.org';
Restart anti spam as user "zimbra": zmantispamctl stop; zmantispamctl start
This tags and kills the spam message. The killed spam message is delivered to email@example.com and not to the user's Junk folder (D_DISCARD). Make sure you set $sa_quarantine_cutoff_level to a high value bacause else the message will not be quarantined and sent to firstname.lastname@example.org