By default below are the AntiSpam Tools being offered in Plesk control panel
1) SpamAssassin spam filter
It is a powerful spam filter that uses a wide variety of local and network tests to identify spam signatures.
Please refer to this link for SpamAssassin spam filter configuration.
2) DKIM
DKIM is a spam protection system based on sender authentication. When an email claims to originate from a certain domain, DKIM provides a mechanism by which the recipient system can credibly determine that the email did in fact originate from a person or system authorized to send email for that domain. If the sender verification fails, the recipient system discards such email messages.
Please refer to this link for DKIM configuration.
3) DNS blackhole lists
This spam prevention system is based on DNS queries made by your mail server to a database, which contains known and documented sources of spam, as well as an extensive listing of dynamic IP addresses. Any positive response from this database should result in your mail server returning a ‘550’ error, or rejection of the requested connection.
4) Sender Policy Framework SPF (only available only for Linux hosting)
This spam prevention system is also DNS query-based. It is designed to reduce the amount of spam sent from forged email addresses. With SPF, an Internet domain owner can specify the addresses of machines that are authorized to send email for users of his or her domain. Receivers that implement SPF then treat as suspect any email that claims to come from that domain but fails to come from locations that domain authorizes.
By default all our shared hosting account is predefined with SPF record.
5) Black and White Lists
Black and white lists are standard mail server facilities. You can use black and white lists to block or receive mail from specific servers. Your mail server retrieves domain names and IP addresses of servers which attempt to establish connection with it. If a domain name is matched against black list entries, your server refuses the connection. Thus, the potential spam message will be never received. If an IP address is matched against white list entries, your server receives a message from the sender without using the spam protection systems such as sender authentication, greylisting, or DNSBL.
Please refer to this link for configuring Black and White Lists
6) Greylisting (available only for Linux hosting).
Greylisting is a spam protection system which works as follows: For every email message that comes to the server, sender’s and receiver’s email addresses are recorded in a database. When a message comes for the first time, its sender and receiver addresses are not listed in the database yet, and the server temporarily rejects the message with an SMTP error code. If the mail is legitimate and the sending server is properly configured, it will try sending email again and the message will be accepted. If the message is sent by a spammer, then mail sending will not be retried: spammers usually send mail in bulk to thousands of recipients and do not bother with resending.
Please refer to this link for configuring Greylisting