Spam filters change. Deal with it.

“But I didn’t change anything!”


We’ve all heard it (and maybe even said it). When your mail suddenly starts landing in the spam folder with one or more mailbox providers, the first response is often to point the finger at the mailbox provider or even your own Email Service Provider, since you just know nothing changed with your mailing program. However, even when you don’t think anything has changed, there are often many unseen factors that can make or break your email deliverability.

Sure, whether or not your mail reaches the inbox – or even gets rejected by the recipient – is often affected by things that are easy to see. Changes like sending to a new list, adding IP addresses or domains, or trying out all-new message content are easy to pinpoint when delivery issues arise. But they’re not the only factors that cause failures.

The performance of your mailings can change almost daily, and can be one of the biggest factors in how your mail gets delivered. User engagement, both positive and negative, plays a huge role in inbox rates. If users are opening your mail, moving it into the inbox or Primary tab, assigning a label, responding, etc., that positive engagement is more likely to improve your inbox delivery. If users ignore your message, move it to a bulk folder, or lodge a spam complaint, it could spell bulking or even rejection due to negative engagement.

You probably already know all of this, right? Every email blogger in the world has drilled engagement into your head. But don’t let your eyes gloss over just yet…

What you may not be considering is that these behavior patterns can change without any major change on your part. Maybe the offers in the past couple of emails haven’t been as appealing to your customers, so they’re not opening. Or your business is more seasonal, and engagement rates are lower due to the time of year. And what about other factors that may increase spam complaints, like general email fatigue around holiday seasons? All of these factors can affect where your message lands, though they may not be the most obvious at first glance.

But let’s assume for a minute that you’re right – absolutely nothing on your end has changed. Your open rates are identical, content is constant, and no seasonal malaise has taken hold. Even if true, that’s only one side of the coin. Mailbox providers, ISPs, and spam filter operators regularly change their filtering criteria, which could send your mail from inbox to spam folder at the flip of a switch. Some providers, like Gmail, are “smart” about these changes and base the adjustments on observed user behavior and complex algorithms. In fact, many of the factors that impact delivery at Gmail can change almost daily, based on mailing patterns.

At the same time, many providers make more arbitrary changes – based on observed data as well, but not quite as fluid as those at Gmail et al. These changes might include lowering a spam complaint threshold, or even turning on new spam trap addresses. Often the major blacklist providers like Spamhaus will monitor spam trap addresses for traffic before actually making them active spam traps. Even though you are mailing an address that wasn’t a spam trap yesterday, it might become one today.

As a sender, you simply need to take precautions to ensure your email program is resistant to these changes. If a small change in engagement or filtering criteria is enough to derail your inbox rates, then it’s likely you weren’t following best practices before the change. If you are getting clear permission, monitoring and targeting your most engaged contacts, and cleaning your list of outdated and dormant subscribers, you’re on the right track. But to get the most effective insurance against these changes, you should be watching engagement and list hygiene regularly. Check engagement quarterly or even monthly. Measure which types of content or sending frequency generate the most (and least) engagement.

Even so, there will be times that even those best practices are not enough to navigate the muddy waters of email delivery. Fortunately for you, there’s a whole segment of the industry who specialize in email delivery, privacy and compliance.

To misquote a famous tome, “Those who can, do. Those who can’t, hire an expert.”

– BG


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