Configure spam filtering for a mailbox

Before changing

Confirm the mailbox is hosted in Plesk

This guide applies when the address receives mail on a UKC Plesk hosting server. If the domain's MX records point to Microsoft 365, Google Workspace or another provider, configure spam protection there instead.

Check the Spam folder and any existing mail-app rules before changing server filtering. A message can be moved by either layer.

Choose safe handling

Keep suspected messages recoverable

• Move to Spam: best for most IMAP users because suspected messages remain available for review.
• Mark the subject: useful when a desktop mail application will sort messages using the spam label.
• Delete automatically: carries the greatest false-positive risk and is not recommended while tuning.

Plesk steps

Enable the filter

1. Log in to the correct Plesk service. Use “Log in to Plesk” from the hosting service in your UKC Client Area.
2. Open Mail. Select the complete email address, then open its Spam Filter tab.
3. Enable spam filtering. Select Switch on spam filtering for this email address.
4. Choose what happens to suspected spam. Prefer moving it to Spam or marking the subject while testing.
5. Save the settings. Send normal test mail and review classification over the following days.

Sensitivity

Lower numbers classify more mail as spam

Plesk commonly starts with a score of seven. If too much spam reaches the Inbox, reduce the value by one. If legitimate mail is being marked as spam, increase it by one. Wait several days between adjustments so the result is meaningful.

Sender rules

Use allow and block lists narrowly

Add a specific trusted sender to the allow list only when messages are consistently misclassified. Add a persistent unwanted sender to the block list when normal filtering is insufficient. Avoid allowing or blocking an entire domain unless every address under it should receive the same treatment.

Sender addresses can be forged, so an allow-list entry is not a substitute for checking suspicious links, attachments or payment requests.

Improve accuracy

Review and train through IMAP

When server training is available, move spam from Inbox to Spam and move legitimate messages from Spam back to Inbox using webmail or an IMAP mail application. Continue reviewing the Spam folder regularly and remember that retention may remove older messages automatically.

Troubleshooting

When a message is still misplaced

• Search Spam, Inbox and mail-app folders before deciding it was not delivered.
• Inspect the full message headers for spam score and authentication results.
• Confirm whether Plesk or the receiving mail application moved it.
• Check mailbox quota and forwarding rules.
• Test with a new uniquely titled message rather than repeatedly resending the same one.

Need help?

Send a traceable example

Include the affected mailbox, sender, exact subject, date and time, where the message appeared, current sensitivity and the full message headers or non-delivery response. Do not forward passwords or suspicious attachments.