Once upon a time (about 15 years ago), avoiding email filters was pretty easy. Almost every filter in existence was based on a stored database of words and phrases that were labeled as “bad.” If you used these words and phrases in your email, your mail was unlikely to get delivered to the inbox – if at all.
As time passed, spammers began to get more sophisticated with their methods, modifying the content of their messages just enough to evade these filters. The spam filters changed as well, but it seemed like the spammers were always a step ahead of the database updates. Most spam filter operators realized that a database of banned words, or spam words, would not be enough to catch the ever-changing deluge of spam messages, and new technology began to emerge.
In the early 2000s, the use of Bayesian spam filtering technology became more popular. Bayesian filters could be ‘trained’ to determine the probability that a certain message contained spam words based on the words included in the message. On the basis of this technology, Internet Service Providers (ISPs) and filtering providers built the much more complex anti-spam systems we see today.
Actions speak louder than words.
Modern anti-spam systems are typically based on a combination of factors, with the most prominent being engagement. Positive engagement (opens and clicks) make a message more likely to be delivered to the inbox, while inactivity and negative engagement (spam complaints) decrease the likelihood of inbox delivery. Content still plays a part in delivery, but in a slightly different way than in years past.
Now many spam filters take an aggregate of all the messages received by their servers, looking specifically at those marked as spam. Based on all of those emails, the filter will create a composite (sometimes called a “fingerprint”) that identifies the characteristics most commonly found in messages containing spam words. Messages that match this composite with a certain degree of similarity are determined to be spam and do not reach the inbox.
The primary difference between content filtering of old and today’s filtering is the dynamic nature of the new technology. Whereas previous generations of filters would have a mostly static database of words and phrases to avoid, today’s filters have the propensity to change at will as different types of messages become more and less prominent. This means that, at any given time, the words and phrases that could flag a message as containing spam words might be different.
However, there are some common threads running through both methods of content filtering. Many familiar spam topics that triggered filters way back in the 1990s are still around today, and messages referencing those topics are still more likely to get flagged as spam by today’s filters. Legitimate senders advertising these types of products (financial services, adult products, and anything pertaining to Nigeria are a few examples) need to closely follow opt-in and list management best practices to avoid issues.
Follow the rules.
The good news for email marketers is following best practices for list acquisition and hygiene is the most effective way to maximize inbox delivery rates. Sending relevant, timely content to subscribers who have opted in and have a history of engaging with your content will almost invariably lead to high inbox rates.
If you’re already managing your list effectively but still worry you may run afoul of an ISP content filter, one of the best things you can do is the most simple: peruse your spam folder. Even reading through a couple dozen subject lines will give you a good indication of the types of spam messages that are most prevalent at the time. If you see a pattern of subject lines or content that closely mirrors your own, it may be good motivation to consider a content revamp.
No amount of knowledge or experience can guarantee your messages will reach the inbox, but if you follow best practices, the odds are greatly in your favor. The WhatCounts team can also provide guidance if you have questions. If you are seeing engagement rates drop at a particular ISP, reach out to your Strategic Account Manager or Technical Account Manager today. If you need an additional boost, whether it’s delivery monitoring or revising a template to better drive engagement, our Delivery and Campaign Production Services teams can help with additional services.