Delivery occurs when a message is accepted by the receiving server (inbox provider).
When we talk about delivery rate, we're talking about the percentage of email that was actually delivered to the intended subscribers. As long as a message is not bounced, it's considered delivered.
Deliverability, on the other hand, refers to where a message lands after it's been accepted/delivered. Does it get placed in the subscriber's inbox or is it dumped in spam?
80% of deliverability is influenced by your reputation as a sender, and the other 20% is the content of what you send. Why that breakdown? Your reputation as a sender is predominantly influenced by the behavior of your subscribers, while the content is analyzed by machine algorithms (think spam filters). Because inbox providers care more about humans than machines, your sender reputation will always carry more weight.
Key Deliverability Players
Your email service provider, or ESP, is the system you use to send your emails.
Inbox Provider & ISPs
The inbox providers are the governing bodies. They protect their customers' (your subscribers') inboxes from the estimated 70% of spam email that gets sent. These are the Gmails, Yahoos, and Outlooks of the world. Internet service providers (ISP) like Comcast, AT&T, and Charter, can also be inbox providers. It's in the Inbox Provider & ISP's best interest to reduce the risk of bad emails getting through while minimizing their hosting and data costs, which is why they are so strict.
Your subscribers are who you send to. How they interact with your email is ultimately the most influential signal back to the inbox providers, so it's up to you, the sender, to keep them front and center in any strategies you devise.
How Subscribers Impact Deliverability
What your subscribers choose to do with your email forms the primary basis by which inbox providers evaluate reputation and, thus, decide inbox placement.
Ultimately, you want to optimize for your subscribers to engage with your emails in a positive way - replying to what you’ve sent, adding you to their address book, marking your emails as important, or engaging through opens and clicks.
Opens are increasingly important, as inbox providers will negatively mark reputation if your emails are routinely unopened by your subscribers. If you're sending a campaign, strive for an open rate above 17% to ensure your emails aren't lingering as unread.
While deleting or opting out may feel like negative actions, and en masse they can be, they don't necessarily reflect poorly on your sending practices, just that the needs of the subscriber has changed.
Emails marked as spam or moved to the spam folder, however, are the actions to watch out for the most. While emails being initially placed in the spam folder is driven by the inbox provider, being marked as spam from the inbox tells the inbox provider that your subscriber believes you are spamming them, and their algorithms are more likely to categorize you as a spammer. Watch out for complaint rates above 0.02%.
Read this related article on Email Deliverability best practices.