How to Set Up Spam Filtering in Plesk

Plesk includes SpamAssassin, a server-side spam filter that scans incoming emails and scores them based on spam characteristics. You can configure spam filtering per email address to control how spam is handled. This guide covers setting up and fine-tuning spam filtering.

Enabling Spam Filtering for an Email Address

1. Log in to Plesk.
2. Go to Mail.
3. Click the email address you want to protect.
4. Go to the Spam Filter tab.
5. Select Switch on spam filtering for this email address.
6. Choose how spam is handled:
   • Mark spam messages by adding text to subject: Adds a label (e.g., *****SPAM*****) to the subject line. You can then set up rules in your email client to sort these messages.
   • Delete all spam messages: Automatically deletes emails identified as spam. Use with caution — legitimate emails may be deleted.
   • Move spam to the Spam folder: Moves spam to a Spam IMAP folder. Messages in this folder are automatically deleted after 30 days. Review regularly to catch false positives.
7. Click OK.

Adjusting Spam Filter Sensitivity

1. On the Spam Filter tab, click Show Advanced Settings.
2. In the Spam filter sensitivity field, set a value:
   • Default (7): Balanced for most situations.
   • Lower values (4-6): More aggressive — catches more spam but may produce more false positives.
   • Higher values (8-10): Less aggressive — fewer false positives but more spam may get through.
3. Click OK.

Whitelisting and Blacklisting

To allow specific senders through or block specific domains:

1. On the Spam Filter tab, find the White list and Black list fields.

Whitelist (trusted senders):

• Enter email addresses or domains (e.g., [email protected] or *@trusted.com).
• Emails from these senders will not be marked as spam.

Blacklist (blocked senders):

• Enter email addresses or domains you want to block (e.g., [email protected] or *@spamdomain.com).

Training the Spam Filter

If you use the Move spam to the Spam folder option with IMAP access:

• Move spam messages from Inbox to the Spam folder to help the filter learn.
• Move legitimate messages from Spam back to Inbox to reduce false positives.
• Over time, the filter becomes more accurate for your email patterns.

Important Notes

• The "Move spam to Spam folder" option only works with IMAP connections, not POP3.
• Messages in the Spam folder are automatically deleted after 30 days. Review this folder regularly.
• If SpamAssassin is not enabled on the server, contact your hosting provider.

Troubleshooting

Legitimate emails are being marked as spam:

• Add the sender to the White list.
• Increase the spam filter sensitivity value.

Spam is still getting through:

• Decrease the spam filter sensitivity value.
• Add the spam source to the Black list.

Spam filter option is not available:

• SpamAssassin may not be enabled on your server. Contact your hosting provider.