Plesk SpamAssassin setup:
Plesk can be configured to have server wide spam configuration applied or on a per account basis. To do so,follow the steps below:
1- Login to Plesk 2- Go to 'Tools and Settings' 3- Click on 'Mail Server Settings' and then click on 'Spam Filtering' 4- Now you can see two options * Switch on server-wide SpamAssassin Filtering or * Apply Individual Settings to Spam
You can decrease the SpamAssassin score and this will more strictly police the emails.