This is a question that has been asked for a very long time. I’m sure when asked, you’ll get the runaround or an answer that doesn’t feel satisfactory. This is because figuring out why an email went into a spam folder is like trying to solve a murder mystery with no smoking gun.

First, we need to understand how an email is sent. When an email is created, it first needs to be copied for all the individual contacts you’re sending to. Then it travels through the internet until it finally reaches your subscriber, but there is a gate with a security guard in the way. That’s the spam filter and he’s making sure that only the qualified emails are getting through. What is considered a qualified email?

Unfortunately, there are many different criteria for a qualified email. Yahoo has its own criteria and so does Gmail. This is not to be mistaken for Gmail’s smart labels (promotions and social tabs), that’s a different story. There are also private domains, that will have their own criteria. They will usually have subscribed to services like Spamhaus to reject emails based on their own qualifications, and Spamhaus is a well-known spam fighting, non-profit organization. Spamhaus also publishes blacklists that will cause emails from senders on that list, to be automatically placed in spam.

Blacklists are the worst case scenario, though, and when you use a service provider, they will give your warnings before you land on a blacklist. Now that we know how an email is sent, there are normally two reasons why an email lands in the spam folder:

  • Email Content
  • Sending Speed/Frequency

Email content is important because how your email is coded, what words your use, and how it looks all matters when it comes to deliverability, or whether your email goes into the inbox or spam box. When creating your email, for each image you may want to add a couple lines of text. Balancing out images, hyperlinks and text so that there’s not too much of either one. Of course, avoid using symbols, all caps and words that might involve a Nigerian prince.

This is not widely known, but how often your send and how fast you send also matter. If your email was meant to be sent monthly, send monthly! Don’t be sporadic with your sending because it makes you, in a sense, “unreliable” to your subscribers and can lower your sending reputation. Your sending reputation determines whether an email may be accepted or rejected altogether. For those who are in a grey area, they may be sent to spam.

Sending speed surprisingly plays a role. By sending way too fast, your email can be rejected entirely. It will show as “deferred” in your bounce logs. There are some services that may accept the email still, but according to reports from support, it can also land in the spam folder. After an email gets past the filter, we don’t actually know whether it lands in the spam folder. However, we do receive reports from our users and their subscribers. We know how emails are judged and sent, we don’t have concrete evidence to say definitively why an email went to spam.

With public domain users like Gmail, Yahoo, and AOL, we’ll probably never know why. They don’t have any obligations to report that information to the senders. I recall seeing Gmail may generally state why an email may be in the spam folder. For Private Domain users, your IT manager who manages your emails may be able to find out, if they log that information. It could all just be automated for some. So a lot of times when this question gets asked, it’s very difficult to answer because there is no smoking gun.