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Mail Anti-Spam

The antispam software works in conjunction with your mail server. The software identifies spam using a wide range of algorithms on e-mail headers and body text.


If you did not select this module to be included during the installation process, you must first install the module.

You can find this feature in the menu system at the following location:

Server|Mail Scanning|Antispam

Antispam Updates and ClearSDN

The open source SpamAssassin solution is the antispam engine used in ClearOS Enterprise. This software automatically checks for base-only updates on a weekly basis. This is already included in ClearOS Enterprise for free!

In addition, the ClearSDN Antispam Updates service provides additional daily signature updates to improve the effectiveness of the antispam system. These signatures are compiled from third party organizations as well as internal engineering resources from ClearCenter. We keep tabs on the latest available updates and fine tune the system so you can focus on more important things.


Discard Policy (Block Policy)

If you want to discard spam before it reaches mailboxes, you can configure the mail discard policy. For example, you can discard spam marked with high probability (or higher) by using this tool.

Subject Tag

  • Use Subject Tag - enable/disable e-mail subject tag when e-mail is marked as spam
  • Subject Tag Threshold - spam score required to trigger a change in the e-mail subject
  • Subject Tag - the subject tag to use when e-mail is marked as spam

A subject tag can be added to messages marked as spam. For instance a spam message with the subject “Premier Invest0r Rep0rt” will be transformed into “[SPAM] Premier Invest0r Rep0rt”. This feature makes it easy for end users to identify and filter spam.

Image Processing (OCR)

Enabling Image Processing will improve the spam identification rate for spam messages containing images. Using OCR (Optical Character Recognition), antispam engine will convert images to text and perform analysis on the word content of the image.

White and Black Lists

  • White List - a list of e-mail addresses that should never be marked as spam
  • Black List - a list of e-mail addresses that should always be marked as spam

The antispam engine includes both white and black lists. The white list is used to mark e-mail addresses that send non-spam, while the black list is used to mark e-mail addresses that are known spam. Entries should be listed one per line.

Among others, newsletters and legitimate e-commerce e-mail can sometimes be marked as spam. The e-mail addresses for these messages can be added to the white list to prevent the message from becoming marked as spam.

E-mail addresses in the white and black lists can use the * wildcard character to match any characters. For instance, * and *.gov will mark all e-mail from the and .gov domains.

Improving Effectiveness - Spam Training

You can improve the effectiveness of the antispam systems on your ClearOS system by identifying:

  • Messages that were spam, but not identified as such
  • Messages that were innocent, but identified as spam (false positive)

With a week or two of diligent training your system with these messages, you can expect to see a more effective antispam engine. There are two ways to train the antispam systems on your ClearOS system: webmail and mail-forwarding.


Training the antispam system via webmail is simple and more effective. In the Webmail interface, simply select the messages that you wish to process and press either the or buttons. You will then be shown a confirmation message before the actual processing takes place.

E-mail Forwarding

Training via e-mail forwarding is not as effective since information is lost when you forward a message. If you decide to use this method, there are two e-mail addresses used for training:

  • – e-mail address for messages incorrectly identified as spam
  • – e-mail address for spam that was not identified as such

In order to use this style of spam training, messages should be forwarded as an attachment.

content/en_us/5_mail_antispam.txt · Last modified: 2015/03/02 09:09 (external edit)