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Knowledgebase: Spam/Email Filters
Email Filters - An Overview
Posted on 20 November 2003 05:26 AM

FutureQuest® offers Site Owners the ability to use filters on their email accounts, providing the ability to bounce, delete or redirect incoming email, based on certain conditions. The FutureQuest® CNC Email Manager offers built-in email filters, designed to be point-and-click simple, including SpamAssassin, for identifying junk email. For those Site Owners who desire more advanced filtering options, FutureQuest® offers the ability to implement your own custom filters. There are three main types of filtering options. These types are:

A powerful program designed to recognize and tag email that has the same traits as spam. FutureQuest® has pre-installed this software for all full package Site Owners and provides options for handling any emails tagged by SpamAssassin. Options provided include customizable subject tags and deleting or redirecting the tagged email. Scroll down for details on how to use FutureQuest's built-in SpamAssassin filters.

Built-In Filters
Pre-installed email filters that can be set up by simply filling in a web based form from within the CNC Email Manager. Capabilities of the Built-In filters include the ability to delete, bounce, or redirect emails that contain pre-selected and user defined types of file attachments, messages over a certain size, or messages sent via a specified IP address or from a particular SMTP sender. A system-wide filter is always enabled that scans all incoming email and rejects messages with a detected virus, preventing them from entering the FutureQuest network! You will find a detailed description of FutureQuest's Built-In Email Filters below.

Custom Filters
Provide advanced filtering options for FutureQuest® Site Owners who want to run their own scripts and programs on incoming email. Using such filters, Site Owners can have extremely flexible and powerful control over their email.

FutureQuest® offers two tutorials under the topic of "Custom Filters":

  • Filter Recipes: Copy-n-Paste examples to help Site Owners set up some of the more commonly requested one-liner shell script filters. Some of the included examples show how to bounce, forward, or redirect incoming email, based on a variety of test conditions. In the Filter Recipe Cookbook, we provide a collection of common filter "recipes" that can be copied or adapted to suit your needs.

  • Advanced Custom Filters: Detailed information about setting up advanced types of filters, including custom-written scripts or third party email scripts, is available in the Advanced Custom Filter tutorial.
For information concerning the order in which the filters are executed, visit:
FutureQuest's tutorial on Filter Execution Order.

SpamAssassin: Built-In Spam Filtering

FutureQuest® is proud to offer a graphical interface for using the popular SpamAssassin program--said to be "state-of-the-art" in spam filtering software!

SpamAssassin works by running a number of tests from its rules database on incoming email to determine a score for each email. For each rule that the email matches, points ("hits") are added to or subtracted from the score for the email. If the point total for an email meets or exceeds the "Required Score" setting, the email is tagged as spam.

The interface for SpamAssassin is located in your CNC Email Manager. Through this interface, you can choose to enable and configure SpamAssassin for individual email accounts, or globally so that the same settings will be applied to all incoming email for the domain. FutureQuest's SpamAssassin interface will allow you to:
  • Set the Required Score, which is the minimum number of points for an email to qualify as spam.

  • Choose to redirect, delete, or simply "tag" email that SpamAssassin determines to be likely spam. (Note: The option to set SpamAssassin to bounce is no longer being offered and can only be found on accounts that currently have that option set. Spammers rarely use their own email addresses for sending out spam, so bouncing known spam often results in innocent parties receiving the bounce messages and can lead to spam complaints. If you have SpamAssassin set to bounce, please consider changing that action.)

    • Redirecting will allow you to forward tagged email to another email address. (Note: The destination address should be an address on your domain to avoid sending spam to another network and possibly generating spam complaints against your domain and FutureQuest.)

    • Deleted email is permanently removed from the system. You will not be able to retrieve deleted email and obviously should use caution.

    • If you choose to simply tag the email, you can have all email delivered to the account and use your email client to filter on the message headers inserted by SpamAssassin for tagged emails.

  • Choose a customized Subject Tag for inserting into the Subject header of tagged email. This will not apply to messages that are bounced.

  • Enter particular email addresses or domains into a whitelist. An email sent to or from a whitelisted address will have 100 points subtracted from its total score. Drastically lowering the email's score in this manner helps prevent it from being tagged as spam.

  • Enter particular email addresses or domains into a blacklist. An email sent from a blacklisted address will have 100 points added to its total score. Drastically increasing the email's score in this manner makes it very likely that the email will be tagged as spam, regardless of its content.

  • Apply filter preferences for the current mailbox to other email accounts.

  • Disable the filter without losing the preference settings.
To manage the SpamAssassin settings for an individual email account, vist your CNC's Email Manager and click on the username of the email account you would like to configure. You will be taken to that Mailbox's Properties page. From the Mailbox Properties page, click on the "edit" link next to SpamAssassin Filter.

To manage the SpamAssassin settings globally, click on “SpamAssassin Filters” under the Global filters section from the CNC Email Manager screen. (Note: It is not possible to enable SpamAssassin as both a global filter and on individual email accounts. You must choose one or the other.)

For details and a thorough explanation of the configuration options available with SpamAssassin, scroll down to the “Helpful Hints” section of the screen or click the “Hints” link.

Built-In Filters: Point-n-Click Simple

To use the built-in filters, go to the Email Manager section of your CNC and select a particular POP email account or email alias by clicking on the name of the mailbox. This will take you to the Mailbox Properties screen. Next, click on the "edit" link in the Built-In Filters row. This will take you to a page with a list of the different Built-In Filters offered by FutureQuest®. (Note: If you would rather have a Built-In Filter applied to all of your accounts you can enable the built-in filters globally instead by clicking "Built-In Filters" under the Global filters section of the main Email Manager screen. When enabling Global filters, the settings will affect ALL incoming email for your domain.)

Below is a list, including brief descriptions, of the available Built-In Filters. Most of these can be set to bounce, delete or redirect an incoming email:
  • Virus Filter - Always Enabled - This is a system-wide filter that cannot be disabled or modified. The Virus Filter scans all incoming messages, including attachments, for known virus signatures. If a virus is detected the message will be refused, without notice to the intended recipient, to prevent it from being processed and delivered or forwarded to innocent parties.

  • Any Attachments - triggered by messages that contain any attachment with a filename. Attachments that do not have a filename, such as PGP signatures, will not trigger this filter.

  • Executable Content - triggered by messages with attachments containing an executable Window's signature in MIME encoded data, and does not depend on filename for the attachment. This filter can be used in addition to the Executable Attachments filter for added security.

  • Executable Attachments - triggered when the incoming email has an attachment that ends in one of several extensions commonly associated with executable files. The list of file extensions currently blocked is listed in the CNC. Using this filter may help avoid emails containing viruses.

  • Attachment Extensions - allows the Site Owner to specify the particular extensions on file attachments for which the filter is triggered. Extensions can be either whitelisted or blacklisted.

  • Maximum Message Size - triggered when the message exceeds a certain size, as specified by the Site Owner.

  • Mailbox Disk Space Quotas - enables you to define a maximum amount of disk space any email account may consume within your web site's hosting package. This filter will enable you to set hard and soft disk space quotas for each individual email account.

  • Received Line IP Addresses - triggered when an IP address in the email's Received headers matches a pattern specified by the Site Owner.

  • SMTP Sender Addresses - triggered when the SMTP envelope SENDER matches an email address pattern specified by the Site Owner.

  • SMTP Recipient Addresses - triggered when the SMTP envelope RECIPIENT matches an email address pattern specified by the Site Owner.

To configure, click on the filter you wish to edit. For additional guidance, be sure to pay special attention to the "Helpful Hints" contained within the CNC.