By default, the following AntiSpam Tools are available in the Plesk control panel:
1) SpamAssassin spam filter
SpamAssassin is a robust spam filtering solution that employs a variety of local and network tests to detect spam signatures.
For information on configuring the SpamAssassin spam filter, please refer to this link.
2) DKIM
DKIM is a spam protection method that focuses on sender authentication. It allows the recipient system to verify whether an email claiming to come from a specific domain is genuinely from an authorized sender for that domain. If the sender cannot be verified, the recipient system will discard those messages.
For DKIM configuration details, please visit this link.
3) DNS blackhole lists
This spam prevention method relies on DNS queries made by your mail server to a database that holds recognized sources of spam as well as a comprehensive list of dynamic IP addresses. A positive response from this database will lead your mail server to return a ‘550’ error, thus rejecting the connection request.
4) Sender Policy Framework (SPF) (available only for Linux hosting)
This is another DNS query-based spam control method. SPF's purpose is to lower the volume of spam sent from forged email addresses. It enables an Internet domain owner to specify the IP addresses of machines authorized to send emails on behalf of their domain. Receivers that utilize SPF will treat any email claiming to originate from that domain as suspicious if it does not come from the authorized locations.
All our shared hosting accounts come with a predefined SPF record by default.
5) Black and White Lists
Black and white lists are standard features found in mail servers. They can be used to either block or allow emails from specific servers. Your mail server collects domain names and IP addresses of servers attempting to connect with it. If a domain matches an entry in the blacklist, the connection is denied, preventing the potential spam message from being received. Conversely, if an IP matches an entry in the whitelist, the server accepts the message without applying spam protection measures like sender authentication, greylisting, or DNSBL.
For guidance on configuring Black and White Lists, please refer to this link.
6) Greylisting (available only for Linux hosting).
Greylisting functions as a spam protection mechanism in the following manner: For every incoming email, the sender's and recipient's email addresses are recorded in a database. If it's the first time that the message is being sent, and neither address is already in the database, the server will temporarily reject the message by issuing an SMTP error code. If the email is legitimate and the sending server is properly configured, it will attempt to resend the message, which will then be accepted. However, if the message originates from a spammer, it will not be retried, as spammers typically send out mass emails without attempting to resend.
For details on configuring Greylisting, please check this link.