What Are the Different Types of Anti-Spam Hardware?

Anti-spam technology is a counter-attack technology against spam. It has grown in the flood of spam and has produced four generations of technology. Typical anti-spam technologies include basic filtering technology, intelligent filtering technology, and front-end authentication technology. ^[1]

The development of anti-spam technology has mainly experienced the following four stages.

The first generation technology includes basic MTA control, black and white list, keyword filtering, letter header test, header filtering, simple DNS test, IP filtering, keyword filtering, mail (attachment) size control, and SMTP connection time and frequency control.

The second generation technology mainly includes real-time blacklist and electronic signature technology.

The third generation technology is mainly the technology using intelligent methods, such as Bayesian filtering,

Anti-spam technology can be divided into 4 categories-filtering technology, verification query technology, challenge technology and cryptography. These solutions can reduce the problem of spam, but they also have their own limitations.

1. Filtration technology

Filtering is a relatively simple but straightforward way to deal with spam. This technology is mainly used in receiving systems (MUA, such as OUTLOOK EXPRESS or MTA, such as sendmail) to identify and process spam. In terms of application, this technology is also the most widely used, such as anti-spam plug-ins on many mail servers, anti-spam gateways, and anti-spam functions on the client, all of which are filtering technologies.

2. Verify query technology

Spam emails generally use fake sender addresses, and very few spam emails use real addresses. Spammers forge emails for the following reasons: Because it is illegal, in many countries, sending spam is mandatory. By forging the sending address, the sender may avoid being prosecuted; because it is unwelcome, spam Email senders understand that spam is unwelcome. By forging the sender's address, this response can be reduced. Due to restrictions from ISPs, most ISPs have terms of service to prevent spam. By forging the sender's address, they can Reduce the possibility of network access being blocked by your ISP. Therefore, if you can use a similar black-and-white list, you can more intelligently identify which are fake mail and which are legitimate mail, then you can largely solve the problem of spam. The verification query technology is based on this starting point. produced.

3 Challenge technology

Spammers use some automated mailing software to generate millions of messages every day. Challenging technology can hinder the sending of large amounts of spam by delaying the mail processing process. Normal users who send only a small number of messages are not significantly affected. However, challenge technology has been successful only with few people using it. If it is more popular, people may be more concerned about whether it will affect mail delivery rather than hinder spam.

4 Cryptography

The industry has proposed a scheme that uses password technology to verify the sender of the mail. Essentially, these systems use certificates to provide proof. Forged emails can be easily identified without proper certificates. Here are some password solutions.

SMTP (Simple Mail Transfer Protocol) cannot directly support encrypted authentication. Some solutions extend SMTP (such as S / MIME, PGP / MIME, and AMTP), while others intend to replace the current mail system, such as MTP. When using a certificate, such as X.509 or TLS, the certificate authority must be available, but if the certificate is stored in DNS, then the private key must be available during verification, that is, if spammers can access These private keys, then they can generate valid public keys. On the other hand, the main certificate authority (CA) is also used, but mail is a distributed system, and no one wants all mail to be controlled by a single CA. Some solutions therefore allow multiple CA systems. This scalability also allows spammers to run private CA servers.

Without a certificate authority, other ways are needed to distribute keys between senders and receivers. This method is feasible in unconnected networks or in closed groups, but it is not very suitable when used by a large number of individuals, especially in the case of the need to establish new contacts. Essentially, pre-shared keys are a bit like whitelist filters: only people who know each other can send mail. ^[2]