Spam causes many harmful effects, so the prevention and prevent spam is needed. There are several companies providing software solutions against spam, each product line has the features and advantages Nhược individual points, but most products that are based on the activities some following principles:

Using DNS blacklist

Solution of DNS black list will block messages from addresses in DNS blacklist list. There are two types of DNS Blacklist list is often used, is:

• A list of the spam know, the list of this domain are listed and updated at http://spamhaus.org/sbl.

• list of email servers allow or fail to make the transition spam sent from the spammer. This list is listed and updated regularly at http://www.ordb.org. Database Open Relay Database is maintained by a ORDB.org non-profits.

When an email is sent, it will go through a SMTP server before moving to address the recipient. The IP address of the SMTP mail server that has been transferred in the header of the email. The anti-spam program will check all the IP address was found in the header of that email as compared to the database DNS Blacklist know. If the IP address found in this database on the DNS Blacklist, it is considered spam, but if not, email will be considered a valid email.

This method has advantages that email can be checked before downloading, thereby saving bandwidth access. Nhược points of this method is not detected the forged email sender address.

Use SURBL list

Method using SURBL detects spam based on content of the email. Anti-spam Program will analyze the content of the email see inside it contains links have been listed in the Spam URI Realtime Blocklists (SURBL) or not. SURBL contains a list of domain and address of the spammer know. The database is provided and updated regularly at www.surbl.org ..

There are many other SURBL lists like sc.surbl.org, ws.surbl.org, ob.surbl.org, ab.surbl.org …, the list is updated from multiple sources. Typically, administrators often combine the SURBL list by reference to the address multi.surbl.org. If an email after checking content with the link specified in SURBL list it will be marked as spam email, but it will not be for a normal email.

This method has advantages to detect the fake email address sent to deceive filters. Nhược points is email must be downloaded before the test, so will access bandwidth and resources of the computer to analyze the email.

Check with the

Spam attack type “dictionary” to use the email addresses and domains known to create a valid email address other. By this technique spammer can send spam to email addresses of a randomly. Some of the email address of that real, but a large number of which is the address does not exist and they cause the “flood” of mail servers.

Method to check the recipient will prevent this type of attack by blocking the email sent to addresses not exist on the Active Directory on a server or mail server in the company. This feature will use Active Directory or LDAP server to verify the recipient address can exist or not. If the recipient address does not exist exceeds a threshold that (by the administrator set) sent to the email will be considered spam and is blocked.

Check the address

By checking the sender address and recipient, most spam will be detected and blocked. Implementation check the address before sending the email will be downloaded save bandwidth access to the entire system.

Technical Sender Policy Framework (SPF, www.openspf.org) is used to check the address to send email. Technical SPF allows the owner of an Internet domain name using DNS records special (called SPF record) specifies the server used to send email from their domain. When an email is sent to, filter SPF will analyze information in the “From” or “Sender” to check the sender address. SPF will then compare it with the address information has been published in the SPF record of the view that email servers are allowed to send email or not. If email from a server is not in the SPF record that the public has the email that is considered fraud.

IP Block

This method will block email sent from IP addresses known. When an email arrives, the filter will analyze the computer address and send to compare with the list address is blocked. If that email came from one address in this list it will be seen as spam, conversely it will be deemed valid email.

Use Bayesian filters

Bayesian filters work based on the Bayes to calculate probability occurs an event based on events occurring before. Technique similar to that used to classify spam. If some text appear often in spam but not often appear in the regular mail, you can conclude that email is spam.

Before you can filter emails with Bayesian filters, users need to create database of keywords and signs (such as $ symbols, the IP address and domain …) collection of spam and email Invalid other.

Each word or per sign will be a probability value appears, this value based on a calculation of how many from or used in spam, in which the messages are not valid to use. The calculation is done by analyzing the email sent by the user and analyzes the type of spam known.

Bayesian filters to work correctly and are effective, need to create a database of email and spam that match specific business of each company. The database was formed when the filter through the period of “training”. Administrators must provide about 1000 emails and 1000 regular spam filters to analyze the generated data to separate it.

Use Black list / white list

The use of list black list, white list to help filter spam more effectively.

Black list is a database of email addresses and domains that you never want to receive emails from it. The email sent from these addresses will be marked as spam.

White list is a database of email addresses and domains you wish to receive email from there. If the messages sent from the address in this list they are always the last.

Usually the filter is the self-study, when an email is marked as spam, the sender address will be automatically included in the list black list. Conversely, when an email is sent from the company, the recipient address will be automatically included in the list white list.

Check Header

This method will analyze the fields in the header of email messages to evaluate it as a normal email or spam. Spam usually has some characteristics such as:

• To empty the From: or To field:

• School From: email containing not follow the RFC standards.

• The URL in the header and the body of the message containing the IP address is encoded as hex Us / oct or combination as username / password (eg the address: http://00722353893457472/hello. com, @ scammer.com www.citibank.com)

• The title of the email may contain the email address to receive personalized e-mail it. Note when using this email address using the form as sales@company.com. For example when a customer feedback by using auto-reply with the title “your email to sales” may be marked as spam

• Send to a very large number of different recipients.

• The file contains photos that do not contain the words to deceive filters.

• Use language with other languages that the recipient is using.

Based on the characteristics of spam, the filter can filter blocked.

Using Challenge / Response

This feature will request the first confirmation email to the first email they sent, after verification, the email address of the sender added to the list White list and then return to the following email sent from addresses that are automatically through to the filter.

By spammer using email programs automatically and they can not confirm to all email sent, so the email will be verified is considered spam.

This method has limitations as it requires the sender to confirm the new email the first thing they send. Nhược To overcome this, the administrator should only use this method for the email that they suspect is spam.

ROOM TO AVOID Spam

Besides the use of anti-spam filters, the user also plays an important role in fighting “pandemic” spam. Therefore users need to follow some guidelines:

• Always update and the latest software is installed on your computer.

• Make sure all machines are updated software against viruses and spam.

• Use firewall to protect your system.

• Do not answer the email is not the origin. For the spammer, you receive an answer from thousands of email they send is a proven method that effectively. In addition, the reply also confirm that your email address is real and is being used. So your email address will be “valuable”, and the spammer will send more spam.

• Do not send personal information by you (credit card numbers, passwords, bank account, etc. ..) in an email. The spammer and those who through the fraud can create fake websites of organizations, banks … suggest you send your password and some information on your credit card via email.

• Do not respond by email from the press “remove” (remove) or “unsubscribe” (unsubscribe) in the title or content of the message unless the source is reliable (the email marketing directly). This is of primary xao spammer to user responses to their spam. When you receive responses, the spammer not only do not remove your email address from the list sent to more than spam because they know that your email address is active.

• Never click on the link URL or web address listed in the spam even if it guides the recipient unsubscribe. This also allows the sender that your email address is being used and you may receive more spam.

• Use two email addresses are different, an address used for the individual as friends, jobs. An address used to register to become members of the forum, the organization … the address where your email can be misused or sold.

• Do not post your email address in public places (such as forums, message board, chat room …) where the spammer often use utility to collect and search for email addresses.

• Use the email service provides anti-spam tools, such as Yahoo! Mail, Gmail.

• Never forwarded spam to others.

• Move spam to get the system administrator email. Administrator will change the filter so the system will block the email so similar.