Many people who faced the problem of SPAM, wondered:"Why, with all the variety of ways and means for SPAM blocking, the problem does not lose its relevance up to the present day?" . There are three reasons:

• The FIRST reason: to ensure their mutual compatibility all e-mail servers (MTA - Mail Transfer Agent) share the same principles of email processing, i.e. standards prescribed in RFC-772, RFC-780, RFC-788, RFC-821, RFC-974, RFC-1425, RFC-1651, RFC-1869, RFC-2821, RFC-5321 for basic SMTP protocol of e-mail operation (SMTP - Simple Mail Transfer Protocol). More detailed information about the operation of SMTP you can get here. If to describe the principle laid in this protocol in one sentence, it would be read like this: "If the addressee exists, the email message must be delivered.".
• The SECOND reason: the fundamental principles that are laid in the technology of e-mail operation have become the main reason for the appearance of SPAM problem; it became necessary to create tools to deal with it, regardless of the standard of the SMTP protocol:

• Access lists (ACL - Access Control List) became the first and the simplest technique, but with the growth of the Internet, they began to reach a huge size and their individual update manually ceased to bring an acceptable result.
• In the second step of antiSPAM process there were laid foundations of senders verification for their trustworthiness, such foundations include: inspection of the Reverse zone (Reverse Resolving), check of a sender's address on its existence and several other technologies.  They all saved from SPAM for a very short period of time. Soon it became clear that all these protection technologies are becoming more resource consuming and begin to interfere with each other.
• As a result, there appeared a new line of SPAM filtering, External Filters for email servers. Because of their flexibility, they began to be used not only to filter out SPAM, but also to check email by Anti-viruses, etc. Taking into account that External Filters process received e-mail messages, the decision about the "quality" of mail is a result of the analysis of:
  • content of e-mail (syntactic and logical analysis of the content).
  • service information hidden in the e-mail message header (system information hidden from the user).

To date, the syntactic analysis becomes not very effective or very resource-consuming for the servers, because SPAMmers use international transliteration, pictures and other tricks. Low efficiency of External Filters together with the analysis of content in its pure form is caused by the fact that for making a decision a template is needed, i.e. an e-mail message must reach a certain number of recipients until gets into the system which creates templates, trapping mailbox, and by the time of the templates update, the message is usually modified to bypass filters.

• The THIRD reason: To ensure an acceptable level of performance, most of SPAM filtering systems, especially with logical analysis of email messages, require ample resources and extensive infrastructure. As a consequence, they are supplied to customers on a paid basis only, and very often as a part of a more complex product, such as anti-virus. What difficulties this can create:

• • Very often, a limited list of supported platforms and software. That limits the choice of solutions, or forces to adapt an existing infrastructure of the company according to it.
  • To analyze the content of an e-mail message, it must be accepted, and this fact is considered by most SPAM systems as a successful delivery, and their interest in the domain is kept. As a result, the problem is not solved, only its manifestations are eliminated.

Those who cannot afford commercial solutions have to be satisfied with the systems in free access with the efficiency of up to 60-70%. With a combination of several tools and techniques and highly skilled administrator the efficiency can reach 80-90%, with very substantial costs on productivity and speed of email delivery. As a rule, the parity is achieved at the level of 60-75%. This situation only fuels the interest both of the customers and SPAMmers.

.

.

Summarizing all the above, a natural question arises: "What way of controlling SPAM can be considered as the most reliable and effective?".
The answer suggests itself; a filtering method must meet the following requirements:

• High processing speed and / or low resource consumption. To minimize the delays during delivery of email and to reduce requirements for system resources of an email server.
• Efficiency of updating of criteria (signatures) for locking SPAM-email.
• Difficulty of bypassing a lock.
• Simplicity of administration, both during the initial setup and during operation.
  

It is obvious that all these conditions can be met only by a system based on Reputation lists (in our understanding, RRBL - Realtime Reputation BlackList). Here are its main characteristics, which fully meet the above listed requirements:

• For publishing the RRBL (RBL) the DNS service is used, which ensures fast speed of response.
• An update of the database can be performed practically in real time. Currently, our service updates the database with a period of 1-2 hours.
• It is not possible to bypass the service, because the decisions on locking emails are taken only on the basis of the reputation of host IP-address. Thus, if any host on the Internet has proved itself as a SPAMmer and got into the RRBL (RBL), then from that moment all emails sent from its IP-address are not considered as trustworthy and is blocked. So, neither changes in the content and structure of email will allow cheating the blocking system.
  
• The use of this method is extremely simple. The majority of modern email servers (MTA) support the DNSBL technology in the basic configuration.

In spite of all the advantages of the RRBL (RBL) technology, it is necessary to pay attention to a number of limitations that cannot be classified as the shortcomings of the technology itself.

• Basic understanding of the technology of email operation by the administrator of the email system.
  
• Fulfillment of minimum recommendations at initial setup of the email system of a domain, as well as their implementation at its further development.
  
• Respectful relationships between administrators of email systems. A position "If you received SPAM from my email system, it's entirely your problem, and if I have been locked, then be so kind to register my server in the White List." – is not allowed.

To estimate your chances of getting into our list of unreliable addresses and networks, we recommend you to read "Basic principles of formation of the RRBL (RBL)". See below.

.