Email spam filters have recently reached such a level of reliability and efficiency that any further development risks killing off legitimate emails from reaching you.

Photo credit: Adam Ciesielski

However, these filters have not cured the global spam epidemic - it's still a huge business for the unscrupulous organizations that profit from it and you will continue to receive spam email in ever-increasing volume, not because the spam filters your ISP has provided you aren't working properly (they are), but because spammers have discovered other, more devious ways to ensure that their junk reaches you.

Spam filters are much like traditional allopathic medicines, they make an attempt to treat an illness once you've contracted it.

To wipe out spam once and for all, measures need to be taken to ensure that it's killed off before it ever gets near your email inbox. In other words, to vaccinate against it at the very source of the disease, before it can spread and infect. Recent attempts at 'containing' spam in the earliest stages are showing some promise.

In a recent article in Technology Review, entitled "As Spam Filters Improve, Attention Shifts to Containment", some of the steps being taken by the ISP's, the global email gatekeepers, to kill spam off nearer its originating source, are highlighted.

Traditionally, spammers have signed up for email accounts with ISPs, either with legitimate, or fraudulent names. They have then used those mail accounts to mass mail their spam. Once the 'inbound' filters provided to email users have been set to detect these particular spammers, the spam has been blocked and the spammer goes out of business - at least until they signed up for another account.

In order to continue in business, spammers have turned to using viruses to 'recruit' personal computers to do their dirty work for them. If you inadvertently let one of their viruses infect your computer, it will turn it into a spam 'zombie', effectively causing your computer to send out thousands of spam emails without you knowing about it. This is highly effective for the spammers, because the spam is being sent out from a legitimate email account and is therefore both harder to detect and harder to switch off.

The solution lies in preventing spam from ever being sent ('outbound') in the first place, whether from a zombie or any other source.

According to the Technology Review article, some ISPs have been taking steps to do this. Earthlink Inc., is phasing in a requirement that their customers' mail programs submit passwords before it will send out their email. This is, however, a huge task.

"Like most Internet providers, EarthLink previously made sure only that a computer was associated with a legitimate account. Now that viruses can co-opt computers and use them to send spam, that's no longer secure enough.

So Earthlink sent out new software, made automated tools available for download and walked customers through manually changing their mail settings when they called tech support for other reasons. A year into the initiative, EarthLink has 80 percent of its customers converted."

Earthlink, AOL and Microsoft's Hotmail are examples of email service providers who have been taking steps to crack down on spam ever leaving their systems.

The former two have long implemented a technique that forces customers to route their email through the provider's own mail servers, instead of sending messages directly to the Internet. This allows them to monitor outgoing email, trace any problems to specific accounts and even block or place 'speed limits' on email that exceeds some hourly or daily threshold.

Microsoft's Hotmail prompts users to type in random letters/numbers dispalyed on the screen whenever they try to send out large volumes of email.

Outbound filters can also target specific zombies.

Other ISPs are adopting these measures, slowly. The issue for ISPs is that they are businesses. They have been making money from spammers. Following the examples of Earthlink, AOL and Hotmail is costly. Also, there is no immediate benefit for the ISP in blocking outbound messages instead of offering inbound filters to their own customers. With inbound filters, customers can at least see how much spam the filter has cut out. With outbound filters, the very fact that users never receive spam in the first place doesn't visibly demonstrate in the user's email inbox that they've been effective.

There's also the issue that the direct benefits of an ISP blocking outbound email don't necessarily go to the ISP but to its competitors, whose customers might otherwise receive more spam.

Apart from the costs associated with implementing outbound measures and the lack of visibility of any success, outbound filters can also hurt legitimate businesses.

"Businesses and some individuals might have a legitimate need to access third-party mail servers, and being forced to go through their providers' systems might cause their e-mail to be mistakenly tagged as spam by the recipient.

ISPs sometimes grant exceptions for businesses and power users.

AOL has a few thousand customers, out of more than 28 million, who are exempt from caps on multiple mails.

Ultimately, ISPs may require customers with special needs to buy a premium service.

"We don't do that, (but) that would be a possibility certainly," EarthLink's Currie said."

Tackling spam as close to the source as possible is proving effective, however it won't kill spam off entirely until all ISPs follow the example of companies such as Earthlink. This make take time, since there will be a degree of (profit-related) reticence. What will be needed is for those heel-dragging ISPs to have their emails blocked by the more virtuous ISPs, at least until they implement outbound controls.