Setting your SPAM filtering is done in the Plesk control panel https://lnxsvr.eu:8443
Navigate to your domain / website settings, find the MAIL icon. There is one for MAIL en one for EMAIL but the end up in the same place.
Find the email address you want to control and click on it.
In the tabs on the topside you will find the SPAM FILTER settings. Good to open the ADVANCED link because the most important setting is there: Spam filter sensitivity
Default is 7 but the lower the number to more SPAM will be stopped. IF you want to go strong on the it is a good idea not to delete the mails but move them to the junk folder so you can monitor the false positives.
Add senders to the whitelist as needed.
More info also in the help file in the control panel: https://docs.plesk.com/en-US/onyx/reseller-guide/website-management/mail-settings/mail-account-settings.73361/
