Junk mail filtering
Out of the box, Xeams provides an excellent junk mail filtering solution. Upon arrival, every email gets:
- Checked against the sender's IP using several RBLs and SPF rules
- Checked for viruses in attachment
- Content filtering based on user defined rules as well as Bayesian analysis
- Attachment filtering
- Company policy rules
- Finger print analysis
- and more...
By default all quarantined emails are saved on the server for 15 days. All quarantined messages gets stored in a different folder, which are easily accessible by either the web interface or any IMAP client such as MS Outlook and Mozilla Thunderbird.
to learn more about the rules engine in Xeams.
Xeams uses a sophisticated score based mechanism to decide if an email should be considered junk. Every in-coming and out-going email is assigned a score. Based on this score, Xeams assigns one of three categories to the email:
- Possible Junk
Besides Junk and Good, Xeams utilizes a third category called Possible Junk. Occasionally, if an email to too close to being good or junk, it is assigned this category, providing the users to manually decide if they want to mark them as junk or good. By default if an email gets a score less than 60, it is considered good. A score of 100 or higher is considered junk. Score between 60 and 100 is considered Possible Junk.
Scoring is done based on several built-in rules. Every rule in the system can take the score either in the positive or negative direction. The final score decides the category of the email. Rules in Xeams can be further divided into two categories:
- User defined rules
- Self-learning rules
Several user-defined rules are bundled with Xeams at the time of installation. All of these rules has a default score and are fully user configurable.
Self-learning rules adapt to the environment of your users. For example, it learns from the past history of emails to assign a score to future emails. One such rule is called Bayesian Analysis
. Another example of self-learning rule is when a local user sends a message to someone outside the network. Xeams remembers who the recipient is and gives credit to that user if he/she sends a reply back.
Many spam filtering solutions block messages without giving an adequate reason of why it was selected as junk. Xeams, on the other hand, gives a detail description of why a particular email is considered junk. This description is very useful for administrators who want to fine tune the filtering rules.
Types of rules in Xeams for email filtering
Xeams uses several types of rules to assign a score to an email. These rules are defined below.
IP Based Rules
These rules act on the sender's IP address and include the following.
- The word "RBL" stands for Real-Time Blackhole List. It refers to several services on the Internet that keeps a database of IP addresses belonging to known spammers, virus sources and other exploits. Xeams queries these servers to check if the IP address exists in such a list.
- The word "SPF" stands for Sender Policy Framework. It is a mechanism to publish a list of IP address for a given domain. SPF records are used to prevent email forgery on the Internet. Many companies publish their SPF data through their DNS server, which includes a list of IP addresses where an email can originate. Xeams tries to match the SPF record for in-coming messages and assigns a score if a mismatch is found.
- Administrators can either black list or white list IP addresses in Xeams. A black listed IP address is assigned a positive score, whereas a white list IP address is assigned a negative score.
Finger print analysis
- Xeams uses a proprietary method of creating a finger print of every email. This finger print is then compared with future messages to determine if it is part of a bulk-mail campaign.Image analysis
- Embedded images in emails are analyzed for patterns. Body and Header
- Xeams utilizes a two-pass approach to analyze the body of every message. It then compares it with a known list of keywords containing a score. Rules can be specified for the following sections:
Custom filters are the most powerful and effective filters used in Xeams to detect junk messages. Often spammers use several tricks to avoid being filtered. These custom filters are specially designed to detect such tricks. We believe that these custom filters are so effective that leaving just these filters on you can eliminate 90% of all junk messages.
There are two types of virus detection in Xeams
- Finger print analysis
- Integration with CLAMAV - an open source virus protection
Adaptive filters are self-learning filters that
gets smarter by analyzing the patterns of previously sent and received emails. These filters include:
- Bayesian analysis
- Manually marking messages junk or good
- Sender history tracking
to learn more about adaptive filters
Challenge response is a mechanism where the system sends a challenge email to the sender to verify if it is a valid message. This type of filter is disabled by default but can be enabled if the users want to use it.