Sending email shouldn’t be that complicated, right? Let’s talk about a recipient on your list. In this case, we’ll call her “Jane.” Jane sees a piece of content you create and decides she wants to receive your newsletter. She signs up and even confirms her subscription (confirmed opt-in, score!). All of your future newsletters should land in her inbox, no questions asked. Seems simple, right?

I hate to break it to you, but that’s not how it works. There are many moving pieces to the email journey, and hitting “send” is the easy part.

Malicious senders in the form of spammers, phishers, spoofers and [enter other bad-guy types here]—including overly aggressive marketers—have turned the email journey to the inbox into a match of American Gladiator. Walls, flying tennis ball artillery, you name it.

the email journey to the inbox - maze image

To give you a better idea, I’ve outlined a high-level view of what happens when you send mail. While the particulars will vary based on the networks involved, it goes a little something like this:

1. Outbound spam filters (the “artillery”) The email passes through a spam filter before leaving the message transfer agent (MTA). Many email service providers (ESPs) have implemented some form of outbound filtering to protect against malware and phishing attacks that often originate from compromised accounts. Some providers even backup this type of machine policing with human review teams.

2. Blacklists (the “walls”) Before the receiving mail system will even think about accepting a message, it is checked against a number of internal and external IP-based blacklists (a.k.a. a DNS-based Blackhole List) to determine if the sending source is worthy of delivering mail to the mailbox provider. Blacklists like Spamhaus, Barracuda, and SpamCop exist to reduce the deluge of spam.

3. Internal content filters (just when you thought you made it!) Next, the email passes through a content filter on the receiving mail system that is especially designed to smoke out any bad links or attachments, in real time. If any of this content is deemed malicious, your message likely will be rejected entirely.

4. Commercial content filters (yep, more filters) At this point, the email passes through commercial content filters to see if it contains anything left unidentified by earlier gates in the system. You might be surprised at how many of these commercial filters are being used by major mailbox providers. In most cases, failing this step results in a message being filed as spam, rather than rejected outright.

5. Black-box filters (almost there…) Finally, the email is checked against various forms of other filters, especially at providers that offer mailbox-level filtering, to determine if the message should be placed in the inbox or spam folder. And if you’re sending to Gmail, there are also tab placement options besides only hitting the inbox.

And if all of this wasn’t enough, the logic supporting every point in the above list is constantly evolving.

Email deliverability is the term coined for measuring the success of a message reaching its intended recipient. Deliverability, as you can now imagine, is often perceived as a mystical (and sometimes unobtainable) thing because of the complexity involved. You might feel the same way when your mail is placed in Jane’s spam folder or rejected entirely.

The reality is that every serious sender needs the strategy and the tools to successfully deliver mail. Senders need visibility and the actionable data to continuously improve their deliverability.

If you’re curious and want to dive into details about the email journey your mails are taking, 250ok and SparkPost have partnered to provide SparkPost customers with some great tools for analyzing your own inbox performance.


About the Author: 

greg kraios bio

Greg Kraios is a hardcore email nerd and the Founder/CEO of 250ok, the preferred choice for email analytics tools. Before 250ok, Greg spent several years at Salesforce Marketing Cloud (formerly ExactTarget) serving as their ISP Relations Manager, as well as providing deliverability consulting services to a variety senders including Angie’s List, Aprimo and PopularMedia (acquired by StrongView).



10 Steps Great Deliverability Blog Footer