The advanced custom content filtering rules are available for those times when a user may want to provide specific mail handling rules for unique situations. This document won’t attempt to explain how email messages are formatted or what regular expressions are. Rather, it is designed to cover the terminology used in our interface and to document any differences from the standard.

This feature allows you to create custom, advanced string matching filtering rules based on parts of the message. The rules are checked against each email message in priority order until either a match is found or the last rule is processed.

You can match on the following message parts:

Entire Message: Headers, plus the first 20kb and last 2kb of the message body.
Header: Any header item and its value.
Body: First 20kb and last 2kb of the message body.
From: The "mail from:" value. This is not necessarily the same as the "From:" header.
Recipient: The "rcpt to:" value. This is not necessarily the same as the "To:" or "Reply-To:" header.
Subject: The value of the "Subject:" header.

The string operators available are:

Contains: String is located within the message part (case insensitive)
Doesn't Contain: String is not located within the message part (case insensitive)
Equals: String exactly matches message part (case sensitive).
Reg Exp: Traditional NFA (perl) Regular expression, without separators (what's normally between the "/" in perl.)

You are able to specify advanced actions for the match, including:

ACCEPT: Accept the email message (handle it normally).
REJECT: Do not accept message and state the reason for the rejection.
FORWARD: Forward the email message to another email address.
DELETE: Delete the message. No one is notified. The message is just forgotten about.

Creating a Custom Content Filter Rule:

1. Click on the "Edit" link next to "Custom Content Filter Rules".
2. Under "Filter Options", specify a detailed "Name:" and "Description:" that will help you to remember what this rule does.
3. Under "Filter Conditions", specify a message part, an operator, and a string to match on.
4. Optionally click on the "Add Condition" button to add another condition and specify a logical operator of "AND" or "OR".
5. Specify the "Filter Position" for this rule to "Run at": Before Blacklisting: Use this setting when creating rules to "whitelist".
   After Blacklisting: Use this setting when creating rules to "block".
   
6. Under "Filter Action", specify an "Action:" for this rule.

   If you specify "REJECT", you will have to specify the message to include in the rejection email message.

   If you specify "FORWARD", you will have to specify the email address to forward the message to.

7. Optionally, you can add a header item to the message if it is matched using the "Add Headers" fields. Header: The name of a header item to add to the email message. When creating a custom header, please start it with "X-" to be standards compliant. For example, you might specify "X-CustomFilter1".
   Header Content: The content of the header item to add to the email message. For example, you might specify "True".
   

   In the above examples, this would result in a header being added to the message like this:

   X-CustomFilter1: True

   You might use a header like this to tag a specific abusive email message that required special attention. You could then program your email server or email client to take a specific action when it saw messages containing this custom header.

8. Click on the "Add Rule" button to add the rule to your custom content filter.

Changing the priority (order) of your Custom Content Filter Rules:

1. Click on the "Edit" link next to "Custom Content Filter Rules".
2. Select the radio button next to the rule that you want to move up or down in priority (order).
3. Click on the "Move Up" button to move the rule up in priority, or "Move Down" to move the rule down in priority (order).