Protecting Your Mailbox from Spam in Plesk Obsidian

This guide provides comprehensive instructions on how to set up and manage spam filtering for your mailboxes within Plesk Obsidian. By following these steps, you can significantly reduce the amount of unsolicited mail you receive and enhance the security of your email communications.

Note: To further bolster your mail protection against spam and viruses, consider exploring the Plesk Email Security extension, which offers advanced features beyond the native Plesk tools.

Enabling Spam Filtering for a Mailbox

To activate and configure spam filtering for a specific email address in your Plesk environment, follow these detailed steps:

1. Navigate to the Mail section in your Plesk control panel. Select the specific email address you wish to protect, and then proceed to the Spam Filter tab. This tab provides all the necessary settings to manage incoming unsolicited mail.

2. Locate and select the checkbox labeled Switch on spam filtering for this email address. Activating this option is the foundational step to enable the spam protection mechanisms for the chosen mailbox.

3. Determine the desired action for messages that are identified as spam. Plesk offers several options to handle these emails:

   • If you prefer to manage and filter spam using email client software on your local computer, choose the option Mark spam messages by adding the following text to message subject. With this setting, the spam filter will insert "X-Spam-Flag: YES" and "X-Spam-Status: Yes" headers into the message source. Additionally, you can configure the filter to prepend a specific text string to the subject line and optionally add text to the message body, making it easier for your local client to identify and process spam.

   • For those confident in their spam filter's accuracy, you may opt to automatically delete all incoming messages recognized as spam. To implement this, select the option Delete all spam messages. Be aware that this action is irreversible, and messages deleted this way cannot be recovered.

   • (Available only for Linux-based systems) If you access your mailbox via the IMAP protocol and wish for the spam filter to automatically move all identified spam messages into a dedicated IMAP folder named "Spam", select the option Move spam to the Spam folder.

     It is crucial to regularly review the contents of this "Spam" folder, as all messages are automatically cleared from it after 30 days. This ensures that you do not inadvertently miss any legitimate emails that may have been misclassified as spam. Any non-spam messages found here should be promptly moved back to your Inbox folder.

     Furthermore, when the Move spam to the Spam folder option is active, you can actively train the spam filter to enhance its accuracy. This is achieved by moving genuine spam messages from your Inbox into the Spam folder, and conversely, moving legitimate emails that were mistakenly placed in Spam back to your Inbox.

4. Should you observe that the spam filter is either allowing too many spam messages to pass through or incorrectly flagging legitimate emails as spam (false positives), you will need to adjust its sensitivity. To access this setting, click on Show Advanced Settings and then input your desired value into the Spam filter sensitivity field.

   A default sensitivity value of seven is generally effective for most users. However, if an excessive amount of spam continues to reach your inbox, consider decreasing the sensitivity value by one and monitoring the results. If the problem persists, you may reduce it further. Conversely, if important, legitimate mail is being marked as spam, you should increase the sensitivity. It is highly recommended to adjust the sensitivity by no more than one point at a time and to allow a few days for the changes to take effect before making further adjustments. Drastic changes in sensitivity can lead to significant and potentially undesirable shifts in the spam filter’s behavior.

   Note: To achieve even greater accuracy with your spam filter, it is highly recommended to train it using the email messages you receive, as further elaborated in the subsequent section of this article.

5. To ensure that you never miss important communications from specific senders, add their email addresses or entire domain names to the White list field. Emails originating from entries on this list will bypass the spam filter and always be delivered to your inbox.

   Each address or domain should be placed on a separate line, or alternatively, you can separate multiple entries with a comma, a semicolon, or a white space. Wildcard characters can also be utilized for broader inclusion: use an asterisk (*) to substitute for multiple letters, and a question mark (?) for a single letter. For instance: address@mycompany.com, user?@mycompany.com, *@mycompany.com. Specifying *@mycompany.com will whitelist all email addresses associated with the mycompany.com mail domain.

6. Conversely, if you wish to block email from specific domains or individual senders, enter their email addresses or domain names into the Black list field. Messages from these sources will be automatically rejected or marked as spam according to your filter settings.

   Similar to the whitelist, each entry should be on its own line or separated by a comma, a colon, or a white space. Wildcards are also supported here: use an asterisk (*) for a series of letters, and a question mark (?) for a single character. For example: address@spammers.net, user?@spammers.net, *@spammers.net. Entering *@spammers.net will effectively block all emails originating from the entire spammers.net mail domain.

7. For users with Windows-based customer accounts, there is an additional option to specify trusted languages and character sets. Email messages composed in these designated languages and using the defined character sets will be allowed to bypass the spam filter and will not be flagged as spam.

8. On Windows-based customer accounts, you also have the capability to specify IP addresses of individual computers or entire networks from which email should always be accepted without undergoing spam filtering. When inputting network addresses, remember to include a network mask after a slash, for example: 192.168.10.10/24.

9. Once all your spam filter preferences have been configured, click OK to save your changes and apply the new settings to your mailbox.

Enhancing Spam Detection Accuracy

The effectiveness of spam detection can be significantly improved, particularly if the SpamAssassin filter is enabled on your server for your account and you access your mailbox using the IMAP protocol. Active user participation in training the filter is key to optimizing its performance.

To further refine the accuracy of your spam detection system, follow these steps:

1. Access your mailbox using your preferred webmail interface or a desktop mail client program installed on your computer. This provides the environment needed to interact with your email folders.

2. Thoroughly review the messages located in your Inbox folder. Identify all messages that are unequivocally spam and manually move them into the dedicated Spam folder. This action serves as direct feedback to the SpamAssassin filter, teaching it to more efficiently and accurately recognize future spam messages. Conversely, if you find any legitimate emails mistakenly placed in the Spam folder, move them back to your Inbox to refine the filter's understanding of non-spam content.