How do the filters work?
Generally, the filters assign and filter based on points that each message earns. We describe below, several of the settings that determine the points in the default filters.

Messages are assigned a point value depending on various factors, such as number of recipients, whether there are Blind Carbon Copy (BCC) recipients, whether the "Reply To:" address matches the "From:" address, and whether the return address is part of a domain that is notorious for spamming.Messages with a higher point value get blocked, and those with a lower value get delivered to your INBOX.

The accept and reject (white and black) lists use the "envelope address" of the message (i.e. the address the router sees) to filter mail . You can use the Spam Controls site to fine-tune your settings.

Here is a run-down of the 4 levels of settings in the Simplified Interface and their defaults:

Opt-Out
This setting will opt you out of spam filtering. Virus filtering will remain.

BASIC LEVEL
This is the default level of filtering. Our in-house tests have found these filters to be remarkably effective, catching up to 99% of all spam. The risk of legitimate mail being filtered is relatively low.

Quick Summary of BASIC default settings:

• Hit level set at 5
• Check External Blacklists—Yes
• Use Razor—Yes
• Use Bayes—Yes
• All languages are OK
• All character sets are OK

STRONG
The Strong level of filtering implements some rules not used in the Basic filters and has a lower threshold for determining whether or not a message is considered spam. Accordingly, there is a risk that some legitimate emails, especially those that are foreign in origin, will be filtered. We suggest that you review the descriptions above and make changes via the Advanced Options page.

We also suggest that you add to your Accept List addresses of those whose mail you do not want to risk losing. This list can be set up and maintained via the Advanced Options page. Keep a backup of your lists! if you change your level of filtering, you may find it necessary to recreate your address lists.

Quick Summary of STRONG default settings:

• Hits set at 4
• Check External Blacklists—Yes
• Use Razor—Yes
• Use Bayes—Yes
• Some foreign languages are blocked due to the high volume of spam originating from the countries in question.
• Some foreign character sets are blocked due to the high volume of spam originating from the countries in question.

EXTREME
The Extreme level of filter has very broad filtering rules which will catch almost all spam sent to your address. This setting also has the potential, however, to filter a considerable amount of legitimate email. We suggest that you review the rules above and make changes to suit your needs.

As with the Strong level setting, we suggest that you add to your Accept List addresses of those whose mail you do not want to risk losing. This list can be set up and maintained via the Advanced Options page. Keep a backup of your lists! if you change your level of filteing, you may find it necessary to recreate your address lists.

Quick Summary of EXTREME default settings

• Hits set at 3
• Check External Blacklists—Yes
• Use Razor—Yes
• Use Bayes—Yes
• Only English
• Only Western character sets
• Filter all email from the following domains:
  • *@yahoo.com
  • *@msn.com
  • *@hotmail.com
  • *@excite.com
  • *@juno.com
  • *@aol.com

A lot of spam also originates from large national ISPs or free email providers. Spammers sign up for “disposable” accounts at these domains using false identities, send their junk email and then allow the accounts to be closed. Accordingly, the Extreme level of filtering filters email from the domains shown above.