It has been estimated recently that one third of all e-mails transferred from computer to computer are unsolicitated: i.e, spam.
Controlling spam is a challenge, but there are some methods that you can use to reduce spam:
• Use Exchange 2003 filtering features . Microsoft® Exchange Server 2003 offers connection filtering, recipient filtering, and sender filtering to reduce the amount of spam that is sent to users in your organization.
• Educate your users not to respond to or forward spam . Instruct your users not to click any "remove" links included in the mail because the links are often used to verify addresses.
Greylisting is a new method of blocking significant amounts of spam at the mailserver level, but without resorting to heavyweight statistical analysis or other heuristical (and error-prone) approaches. Consequently, implementations are fairly lightweight, and may even decrease network traffic and processor load on your mailserver.
A number of Mail Transfer Agents (MTA) provides techniques to reduce spam. They can block mail from known spammers and spam sites, stop your site being abused by them to act as a relay, etc.
Blacklists:
As the name suggests Blacklists are lists which exclude something. In the case of spam Blacklists exclude IP addresses which are associated with spam and block all e-mails coming from those IP addresses. But how does a Blacklist affect you?
If you have shared hosting on a server, chances are you are also sharing an IP address. An IP address is the numerical representation of where you server is. While humans use alphabetical names to remember a web site; computers and servers don't know where www.xyz.com is but rather know that it is located at 64.191.57.34. The numbers 64.191.57.34 is the IP address of the web site www.xyz.com. Whenever a computer needs to contact www.xyz.com or send mail to www.xyz.com it knows that the IP address is associated to that domain. Now, www.xyz.com is not the only domain (or hosting account) using this IP address. With the aid of server software a single IP address can be reused by more than one domain at a time. This is called virtual hosting. There are many reasons why several domains may be using the same IP address but realize that tens or possibly hundreds of domains may be sharing the same IP address on a server. Now let's examine why this is important when talking about Blacklists.
When a spammer sends out spam, either through a hosting account, or through exploiting a security hole in a server the e-mails are sent from a hosting account which has an IP associated to it. When other computers, and users, find out that they have received spam and they trace the unsolicited e-mail back to the domain which sent the spam. What happens next is that this IP address, which is associated with the spam, is now listed as sending spam and is listed on a Blacklist. What happens next depends on the people running the Blacklists the IP was just listed on.
