Understand ISP-Level E-Mail Filtering
A look at the steps ISPs take to determine the fate of an incoming e-mail message.
A look at the steps ISPs take to determine the fate of an incoming e-mail message.
Got filtered? Of course you have. Your messages have been filtered by ISPs for the past few years.
E-mail filtering is a necessary part of fighting spam. As ClickZ News reported earlier this year, AOL receives roughly 2 billion email messages a day, of which about 75 percent are blocked and another 4 to 7 percent are sent to the bulk folder.
Dealing with this influx of spam is a major issue for ISPs. It’s a tremendous drain on servers and human resources. It’s also a major source of customer complaints, dissatisfaction, and churn. Minimizing the flow of spam to inboxes has become a major point of differentiation as ISPs battle to acquire and retain customers.
Long ago, smart marketers moved past the anger phase, all the way to acceptance. They’re actively deploying a number of techniques to minimize ISP filtering.
Like the search engines’ secretive page-ranking algorithms, ISPs don’t share the specific types of filtering they deploy nor at what thresholds. Through dealing with ISPs over time, it’s apparent there are quite a few key components. Though they may be approached differently at various companies, all are quite commonly used.
ISPs deploy a number of methods to reduce the volume of spam. They may include looking at:
Let’s consider a fictitious, consumer-oriented ISP with 5-10 million subscribers. Typical email filtering happens at multiple levels. It begins before the message even arrives at the ISP’s servers. At the top of the filtering pyramid are:
Large ISPs tend to handle all these steps in-house. Some ISPs contract with anti-spam companies to provide some or all of these services. Most ISPs have unique filtering methods they find work for their needs. They even use their unique methods as selling points.
In upcoming columns, we’ll look at best practices and third-party services that help monitor and resolve ISP filtering issues.
Until next month, keep on deliverin’.
Want more email marketing information? ClickZ E-Mail Reference is an archive of all our email columns, organized by topic.