How to block emails by size using Spam filter in DirectAdmin

How to block emails by size using Spam filter in DirectAdmin

Blocking emails based on their size can be an effective strategy to manage your inbox, especially to prevent large, unsolicited emails from consuming valuable server space or bandwidth. In DirectAdmin, setting up a spam filter to block emails by size involves creating a rule within the spam filtering configuration. While DirectAdmin doesn’t directly offer a built-in, GUI-based option specifically for blocking emails by size through its standard SpamAssassin or spam filter interfaces, you can achieve this by using custom filtering rules or configuring server-wide settings if you have administrative access. Below is a general approach to setting this up:

For Users: Creating a Custom Filter Rule

If you’re a user without administrative access to the server, you might not be able to directly set a size limit on incoming emails via DirectAdmin’s interface. Instead, consider setting up a custom filter rule that targets large attachments, which are often the main contributors to email size. This can be partially achieved with SpamAssassin by scoring emails with large attachments more harshly.

1. Access SpamAssassin: Log into DirectAdmin and navigate to the “SpamAssassin Setup” or “Spam Filters” section.
2. Customize Rules: Look for an option to customize rules or edit a configuration file. You might be able to add custom rules if your hosting provider allows it.
3. Add Rules for Attachments: While you can’t directly filter by size, you can increase the spam score for emails with attachments, which are typically larger. For example:
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   score MIME_BASE64_TEXT 2.5


   This rule increases the spam score of emails containing base64 text, which is often used to encode attachments. Adjust the score as needed.

For Server Administrators: Configuring Exim

Server administrators can set up rules in Exim, the mail transfer agent used by DirectAdmin, to reject emails exceeding a certain size. This requires SSH access to the server.

1. SSH into Your Server: Use an SSH client to log into your server as the root user.
2. Edit the Exim Configuration:
   • Locate the Exim configuration file, often found at /etc/exim.conf or /etc/exim/exim.conf.
   • Open the file in a text editor, such as Nano or Vim.
3. Set the Maximum Message Size:
   • Find the message_size_limit directive. If it doesn’t exist, you can add it to the configuration. For example, to set a size limit of 10MB, add:
     makefileCopy code

     message_size_limit = 10M

   • Save and close the file.
4. Restart Exim: Apply the changes by restarting Exim. The command to restart Exim varies depending on your system but often looks like:
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   systemctl restart exim


   or

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   service exim restart


Important Considerations

• Communicate Changes: If you implement size limits, inform your users so they know about potential restrictions on incoming emails.
• Regularly Review Settings: Overly restrictive settings may block important emails. Monitor blocked emails and adjust your settings as necessary.
• Legal and Privacy Concerns: Be mindful of legal and privacy considerations when handling email communications, especially when filtering or blocking content.

Blocking emails by size can help manage the load on your mail server and prevent spam, but it’s important to strike a balance to ensure legitimate emails aren’t inadvertently blocked. For DirectAdmin users, while direct options might be limited, server administrators have more flexibility to enforce size limits through Exim’s configuration.