Question
How to add an email address / domain / top-level domain to the server-wide blacklist?
Answer
Mark emails as spam with Plesk Email Security extension (if installed)
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Go to Tools & Settings > Plesk Email Security > Server Settings. 
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In the Blocklist field, specify the email address, emails from which will be marked as spam. Note: 
 - To specify a domain, use @example.com
 - To specify a top-level domain, use @.com
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Click Save. 
Mark emails as spam with SpamAssasin
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Go to Tools & Settings > Mail Server Settings > Black List. 
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Click Add Domain and specify the domain name, emails from which will be marked as spam. 
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Click OK. 
Block emails completely on mail server level
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Go to Tools & Settings > Black List. 
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Click Add Domain. 
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Specify the domain name, emails from which will be completely blocked. 
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Click OK. 
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Go to Tools & Settings > Spam filter > Black List. 
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Click Add Domain. 
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Specify the email address, emails from which will be marked as spam. Note: 
 - To specify a domain, use *@example.com
 - To specify a top-level domain, use *@*.com
- Click OK.
For Plesk on Linux
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Connect to a Plesk server via SSH. 
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Add one or multiple domains (separated by comma): # plesk bin mailserver --add-to-black-list example.com 
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View blacklisted domains, if needed: # plesk bin mailserver --info black-list 
For Plesk on Windows Server
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Connect to a Plesk server via RDP. 
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Use one of these commands: - 
to remove unwanted emails from a particular email address: C:> plesk bin mailserver --add-to-black-list [email protected] -action delete 
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to mark unwanted emails as spam from a particular email address: C:> plesk bin mailserver --add-to-black-list [email protected] -action mark_spam Note: 
 - To specify a domain, use *@example.com
 - To specify a top-level domain, use *@*.com
 
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