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Abstract: concern the proliferation of unwanted emails, generally called as spam has been incredibly increased in the last decade. For some users who receive spam email in small quantities its often can be treatable by the user or by the internet service provider (ISP) and rarely poses a significant problem. However ,when spam emails sent in large quantities the both parties of network can found themselves flooded with non avoidable traffic and consequently causes a significant problem .In addition ,unlike usual junk postal mail ,spam emails often includes antisocial contents ,sexual language ,pictures and other kind of advertisements that can be considered offensive for many recipients .Taken the advent of using HTML-enabled email clients ,the spam sender can send an email in HTML format linking it with some java applets that may run automatically when a recipient is reading the email . 
Introduction : computer expertise's found difficulties to define what is spam in terms of the relation between the sender and the recipient , in other words which kind of emails and depending on which base can be considered as spam ,their were a loads of attempts to define what spam is ? .
In the context of computer networks the term "spam" originally referred to a specific kind of Usenet(user network) (NetNews) postings (Baseley 1998) .
Mueller (2003) provides a spam definition that covers both Usenet postings and email: Spam is broadcasting copy of same message through the internet ,trying drive people to read these messages regardless whether people would like to receive the massage or not .The main purpose behind sending spam emails mostly is commercial advertising usually for entrusted products ,all the spam cost is taken from the recipient and ISP represented in the time wasted reading, deleting spam ,congestion in the network and cost of maintenance meanwhile it costs the sender little effort .
Further more ,In order to define spam forms ,the following rules provide some guidance :
â€¢ Sent indiscriminately to multiple recipients.
â€¢ No relationship between the sender and the recipient.
â€¢ Not wanted by most of the recipients.
â€¢ Has some 'payload' that performs an objective of the sender. 
Problems and risk:
Spam emails are sent in huge quantities in various ways and contents, also for different purposes, as follows we will justify the problems caused by spam email depending on its purpose.
1-Advertising spam :this kind of spam usually doesn't harm the user computer ,but try to grab the user intention to some products hi/she might be interested in and not able to buy it from the store ,or try to sell some falsify products .However, there is no much risk reading this kind of spam emails as long as the user doesn't interact with them .
2-Fruad spam : it is email that try to Impersonate the legal authorities that the user might be interacted with like banks ,utility companies and other secure services ,in this spam emails you are told that you have problem with your account and they ask you to re-authenticate your self for security purpose or for updating information etc ,it provides you with link to your legal authority then it redirects the user to a fake web page similar to the original one ,once the user enter his secure information these information is saved and later used by the sender .these kind of spam has major risk on the user and usually try to impose some sanctions like block your account or pay extra tax in order to make you react quickly with .However, this kind of spam has significant financial risk on users ,also known as phishing attacks.
3- Virus spam : in some cases spam hold virus as an attachment file ,often in form of executable file ,once you downloaded your pc is infected ,this exe usually attach in every email you send to be distributed .The risk behind this spam is depending on the user knowledge and understanding how danger to download exe file sent by unknown sender.
4- Voicing particular viewpoints: spam used as a method to justify a viewpoints or debates and some times to announce scientific discovery ,these spam has no direct risk on the user ,but it might be annoying or consuming time and effort deleting them if the recipient not interested. 
In this part we are going to illustrate how to protect our systems against spam emails ,using the two main methods to fighting spam which are filtering and blocking .most of anti-spam products on the market are using a mixed techniques of both mechanisms .these two methods can deployed on both client side (desktop) or server side (mail server ).A new form of defeating spam was introduced by security companies ,is to redirect client email to remote server running anti-spam application ,at this point the anti-spam server's holder will assure that all anti spam measures are applied on the email .Despite of ,what advantages we gain from these two methods ,it does have some weaknesses that may cause potential loss ,which we will discus in the following section
Content-based filtering is technique concern with the email contents including message body , header (From ,To and subject )
Many of spam emails advertise the same type of products and usually tend to use similar vocabulary; as a result we could create a filtering system based on certain words to look into the message body and find matching words. To justify with example, words like "get rich","get green card" or "xxx". However ,this flirting technique could be failed to identify new terms ,based on this point spam filters software should have the ability to extract certain terms that can be used to identify future terms with similar attributes as spam . Another advanced tool used in content filtering system is distributed spam recognition technique ,this tool is relying on peer to peer protocol which allow recipients to use shared identifiers to check the content of the spam .
Companies who run emails server are often carless about spam and don't put much effort filtering spam. some spam emails might appear in spam forms in order to masquerade the origin content of the email .
It's a wide use mechanism to defeat spam ,is blocking the email through the delivery process when the spam email sent from suspicious mail server , based on this knowledge that specific mail server is sending spams ,you might disable accepting any more emails from this mail server .This blocking rule can use the mail server IP address or DNS or other information used during talking with the server .
Lists of "spammer-friendly" mail servers are shared on the internet. Services such as Spamhaus Block List (SBL) allow other servers to check suspicious mail servers in realtime by making an inquiry to SBL over the internet when a suspicious server tries to deliver mail.
The Spamhaus Project (2003b) summarizes the approach as follows:
"The Spamhaus Block List (SBL) is a realtime database of IP addresses of static spam-sources, including known spammers, spam operations and spam support services. SBL listings are based in part on SpamhausRegister of Known Spam Operations (ROKSO) database, spammers which Spamhaus believes are responsible for 90% of all American and European spam". 
Recommendations and Conclusions :
There is no doubt that the range of spam sent every hour are increasing and that spammer-friendly mail servers might develop complicated techniques to defuse spam filtering systems . if this was the case then the current anti-spam scheme is likely insufficient and many clients will certainly flooded by spam emails pushing users to give up using their email accounts . More effort should take a place monitoring all bulk emailres ,and the out come of this action should be studied .on the other hand new proposed laws could help to stop spam spreading problem . its know that there is no long term solutions for spam and often cause negative side effect. Furthermore , using filtering techniques by ISPs ,we advise that the email applications used by the user should be able to support varies technical solutions such as filtering channels and referral networks. These facilities that don't make problem for clients should be activated automatically. if the situation gets worse more risky feature could be used for individuals