Types of Antispam Filters

Sender Policy Framework (SPF) Filtering

SPF extends the Simple Mail Transfer Protocol (SMTP) and Domain Name System (DNS) so mail servers do not accept e-mail unless the sending computer is designated as a legitimate e-mail sender. This feature enables administrators increased capability to stop incoming e-mail from forged e-mail addresses.

Premium AntiSpam

The optional Premium Antispam filter provides automated spam protection in addition to the Standard Antispam filter included in IMail. You can select actions to take if a message is determined to be spam.   

HTML Filtering (Content Filtering)

HTML filtering examines only the HTML portions of an e-mail message, and is comprised of 3 components: an HTML parser, HTML Feature filtering, and a URL Domain Black List. The HTML parser is part of the antispam engine that examines the HTML sections of a message. It extracts the text from HTML tags, and passes the text on to the phrase and statistical filters for examination. The HTML Feature filter allows you to specify which HTML tags you want to consider spam indicators. The URL Domain Black List searches for domain names that occur in the URLs of HTML messages.

Phrase Filtering (Content Filtering)

Phrase filtering searches for common spam phrases within the body and/or subject of an e-mail message and identifies the message as spam. Phrase filtering can be enabled/disabled per domain, and works independently of statistical filtering. For more information see Phrase Filtering.

Statistical Filtering  (Content Filtering)

Statistical filtering examines each word in the body of an e-mail and evaluates whether the word is a statistical indicator of spam. The entire message is then evaluated based on the combined word counts to determine whether it is likely to be spam. You can create a host specific exclude list, specify what action to take when a message is identified as spam, and specify whether to use the primary domain's word counts or create new ones. For more information see Statistical Filtering.

Attachment Blocking Filtering

Attachment blocking filtering lets administrators specify types of file attachments to block from e-mail messages and actions to take on blocked messages. Attachments can be blocked based on message MIME types and filename types. In addition to selecting the types of message attachments to block, you can define actions to take on blocked messages.  

Broken MIME Header Filtering

The Broken MIME Header filter identifies Broken MIME header characteristics that result in SPAM e-mail. You can also define actions to take when Broken MIME headers are identified as SPAM e-mail.

Delivery Rules

You can use domain and user delivery rules to process messages based on the spam X-Headers which are inserted when a message fails a spam test. For more information see Using Delivery Rules to Filter Mail.