Spam Filtering Services

There is a significant market for commercial spam-filtering services. Typically, these are suitable for individuals and small companies that access email via POP3. The different approaches taken by providers are described below.

Collect and Forward

In this approach, the users give their details to the anti-spam service provider. This information includes their ISP details, username, and password. The anti-spam service company then regularly connects to the ISP on behalf of the user and collects all the emails. The spam is filtered out and ham email is forwarded to another POP3 account.

One obvious disadvantage of this approach is that the account username and password have to be passed to another party. It is not wise to give out this sensitive information.

Another disadvantage is that any emails wrongly identified as spam may be lost forever. If the anti-spam service provider provides an archive of spams emails, they can be reviewed and any wrongly identified emails can then be retrieved. Some providers may not provide this service and in other cases, the retention period may be short. Any missing emails will need to be detected quickly to retrieve them before they are purged. Sometimes, this archive feature is offered at an additional cost.

Collect and Return

This is similar to collect and forward but with an interesting twist. Non-spam email is left in the original POP3 mailbox, and spam is deleted from it. The user does not need to change their email client's settings. This is an advantage for the novice user who may be unfamiliar with changing settings on their computer.

This method has all the disadvantages of the collect and forward method. In addition, the anti-spam service provider will check for spam only periodically, and if the user checks their email in between, any spam received since the last check will appear in the inbox. It is not suitable for users who check their email frequently during a day, or those who cannot tolerate even a small amount of spam (for example, accounts for children).

Send and Forward

With this approach, the anti-spam service company provides a new email address for the user. All email should be addressed to this account, where spam is filtered out. Non-spam email is either stored with the anti-spam service provider, or forwarded to a second email address.

The main disadvantage of this is that the user's email address must change, so contacts must be informed. In addition, this may involve the modification of business stationary. If mail is forwarded to another email address, it may still receive spam as spammers often try random email addresses to discover new recipients.

The main advantage of this service is that the anti-spam service provider is in control of most incoming mail and spam is kept at a minimum. This control is lessened when email is forwarded to another account, but a carefully chosen account name may limit the number of spam messages received through spammers inventing user account names.

Choosing an Anti-Spam Service Provider

Behind the scenes, most anti-spam service providers use SpamAssassin or their own proprietary system. They often use extra filters such as Razor, Pyzor, and other paid-for services

If emails are archived by the anti-spam service provider, email storage will be limited and extra space can usually be purchased. Multiple accounts are sometimes available. Web mail access may be offered, which allows users to access email from any machine with a web browser.

Here are some guidelines to choose an anti-spam service provider:

• Use of SSL: Any confidential data should be sent and received via a secure web connection (commonly represented by a padlock symbol in the status bar of a browser). This helps prevent passwords being sniffed, especially when using wireless networking or accessing the Internet in public areas such as an Internet café.
• Background checks: How old is the company selling the anti-spam service? Are they late in filing financial results? Who really owns their domain and net block? Is there any information on the management team? If within Europe, are they large enough to charge VAT? Most of this information can be retrieved from the web with little effort. Background checks like these are also advised when choosing an ISP, a web host, or even when shopping online. It may be worthwhile performing a proper credit check on potential suppliers of software or discussing any concerns with them.
• Service-level agreement: This is hard to wring out of an anti-spam service company. From their point of view, everyone's spam is different and a system that works perfectly for one individual may not work well for another. Blocking spam is difficult as spam is continually evolving. If an anti-spam service company provides an SLA, it should be examined carefully—it may be worthwhile or, on the contrary, be so full of holes that it might as well not exist.

ISP-Provided Services

Some ISPs filter spam but do not advertise the fact. A call to the technical support line will confirm the status of spam filtering.

If an ISP offers a spam-filtering service, then in most situations it is wise to use it. The main advantage of using an ISP service is that there are no changes to existing systems or email addresses. An ISP service may also be cheaper than a third-party service.