Processing Order
The following is the processing order for the anti-spam features. This process assumes that all default options and settings are not altered after installation. Several things can change this order, such as enabling/disabling the "Content Filtering for Authenticated Users" and "Apply to Content Filtering Only" options, but for the most part a message will be processed as follows:
- Trusted Addresses. The IP address (or from address, if enabled) of an incoming message is compared against the trusted address list to see if it matches. If it does match, all other anti-spam checks are skipped. If the IP address does not match, the message is compared against the DNS Black Lists.
- DNS Black Lists. IMail Server initiates connection filtering to compare a message's sender information against configured DNS black lists. If the message matches a black list, it is processed according to whether the black list is a "trusted" or standard black list. If the message does not match a black list, verification checks are performed.
- Verification checks. If enabled, verification tests are performed to verify the "Mail FROM" address, the HELO/EHLO domain, and to perform a reverse DNS lookup. If a message passes all the checks, connection filtering is performed. If a message does not pass all checks, an X-Header is inserted into the message, and the trusted e-mail/domain list is checked.
- Trusted E-mail Addresses/Domains. IMail Server checks to see if the connecting SMTP server's e-mail address or domain is listed in the trusted e-mail Address/Domain list. If it is, the message is delivered. If it is not, the message is passed on to either HTML filtering or phrase filtering, depending on whether it contains HTML code.
- HTML Feature Filtering/URL Domain Black List. If HTML filtering is enabled, the message is examined to determine if it contains any HTML. If it does, it undergoes HTML Feature filtering and is compared against the URL Domain Black List. If the message does not contain any HTML components, this step is skipped and the message is passed on to phrase filtering.
- Phrase Filtering. If phrase filtering is enabled, the message is checked to see if it contains any phrases that are in the phrase list. If the message passes, it is processed according to the settings for phrase filtering. If the message does not pass, it is processed by statistical filtering.
- Statistical Filtering. If statistical filtering is enabled, the message is compared against the spam and non-spam word counts to determine if it is statistically likely to be spam. If it is identified as spam, it is processed according to the settings for statistical filtering. If the message is not identified as spam, it is delivered.
| Note: For information on how the anti-spam features integrate into the mail processing order, see "Processing Order". |
