How to block a particular mailbox or a range of mailboxes belonged to a specific domain from sending emails to Plesk server?
Note: in order to block the email sender by IP, navigate to this article: Is there any way to block an IP address in Plesk Firewall?
To block email accounts on a server-wide level, check out this KB article.
Note: SpamAssassin has to be installed on the server and enabled on the required mailbox.
Go to Plesk > Domains > example.com > Email Addresses > [email protected] > Spam filter.
Click the Show Advanced Settings link.
Specify a particular mailbox or a range of mailboxes belonged to a specific domain in the Black list field, e.g.:
Press the OK button.
Note: The steps above will add the address to individual black list, which will give it a score 100, making it be detected and processed as spam. Now, in order to effectively delete the messages detected as spam, click on "What to do with messages classified as spam" option on the same tab and select the option "Delete all spam messages"
Administrator's guide: SpamAssassin Spam Filter