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An introduction To Email Deliverability

An introduction TO Email Deliverability

What is deliverability and why is it important?

Deliverability is a measure of how many of your emails are going to Subscribers’ inboxes vs their spam folders. After putting so much work into your email marketing, you want to be sure that your messages are actually being seen by your Subscribers! This is why deliverability is crucial.

How is deliverability determined?

There are a lot of factors that influence inbox placement. In general, mailbox providers are trying to determine three things:
Is the message safe?
Is the message wanted by most Subscribers?
Is the message wanted by this particular Subscriber?

If the answer to all three questions is yes, the message belongs in the inbox. If any of the answers above are no, this message belongs in the spam folder. To make this decision, mailbox providers typically turn to the sender reputation they have calculated for you.

Sender Reputation

Mailbox providers, such as Gmail, Microsoft, Yahoo, etc., create a reputation score for your sending domain. You can think of this like a credit score, but unfortunately there’s no one source of truth that can indicate exactly what your score is and why. Mailbox providers keep your score, and the algorithms used to determine it, private. However, the most important determining factor is the way that Subscribers engage (or don’t engage) with your message.

Subscriber Engagement

The best way for mailbox providers to determine where your mail belongs is by seeing how your Subscribers interact with it. There are actions your Subscribers can take that will raise your sender reputation, and actions that will lower your sender reputation.

Here are some recommendations for promoting positive engagement:

List Health

  • Only import Subscribers who have given you direct permission to receive email marketing. Quality is much more important than quantity when it comes to email marketing. You don’t want anyone on your list who doesn’t want to be there. For the best deliverability, be sure everyone on your list knew exactly what they were signing up for.
  • Secure your Forms with a double opt-in and/or ReCaptcha. If your Form isn’t secure, there’s a good chance you’ll start to see bots abusing it. We talk more about why this is harmful to your deliverability here.
  • Prune your list regularly. Be sure you don’t let Cold Subscribers pile up. If you don’t clean your list regularly, the unengaged Subscribers will start to become the majority. When this happens, your sender reputation drops and more messages start to be filtered to spam. Learn more about how to prune your list here.


An important component to your sender reputation is consistency. If there is any sudden change to the way you send messages, mailbox providers will see your messages as risky and potentially place it in the spam folder. Here are some characteristics you’ll want to keep consistent:

  • Sending Domain: It’s perfectly fine to send from multiple domains, but be sure the domain you’re sending from is the domain that Subscribers will recognize. Avoid sending from a brand new domain or a domain that has not sent any mail in a long time (over 6 months).
  • Volume: Be sure to send to a consistent number of Subscribers each week. It’s normal for your list to shrink and grow, but try not to have any major volume swings. (You don’t want to go jump from 5,000 Subscribers to 20,000 Subscribers overnight!) If you need to introduce a large number of new Subscribers, be sure to start sending to them in small batches so you don’t alarm mailbox providers.
  • Frequency: Send at least once per month to keep your sender reputation established. If mailbox providers don’t see enough mail from you, they won’t be able to maintain a reputation for you and you’ll be starting from scratch on your next send. Also, be sure not to send too frequently to Subscribers — it could cause them to mark your messages as spam! We recommend asking your Subscribers ahead of time how often they’d like to hear from you and give them the ability to modify their preferences in each email.


Influence mailbox providers to place your messages in the inbox by becoming Subscriber-focused. Give your Subscribers the power to choose the type of content they want to receive and how often they want to receive it. Build a list of Subscribers who want to be there, and create the kind of content that keeps them engaged!

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