Step 1: Navigate to Tools & Settings > Spam Filter.
Step 2: Choose “Switch on server-wide SpamAssassin spam filtering.”
Step 3: Select “Apply individual settings to spam filtering” for user preferences.
Step 4: (Plesk for Linux) Set resources for SpamAssassin in the “Maximum number of worker spamd processes to run” field.
Step 5: Adjust sensitivity in the “The score that a message must receive to qualify as spam” field.
Step 6: Set the maximum message size:
For Plesk on Windows, choose “Do not filter if mail size exceeds specified size” and set the value.
For Plesk on Linux, edit the /etc/psa/psa.conf file.
Step 7: Specify marking for recognized spam in the “Add the following text to the beginning of the subject of each message recognized as spam” field.
Step 8: (Plesk for Windows) Specify trusted languages and locales.
Step 9: Review configured settings.
Step 10: Save changes by clicking OK.