Email Deliverability 101

Modified on Tue, 06 Dec 2022 at 12:29 AM

Email deliverability is the measurement of emails that go to your Subscribers’ inboxes vs. spam/junk folders. You want to ensure your emails end up in your Subscribers’ inboxes, so high deliverability should be a critical focus.

You have the power to promote high deliverability by being Subscriber-focused. Send content consistently, and send content that they will actually want to engage with. Give them the power to choose how often they hear from you, providing opportunities for authentic engagement. All of these positive drivers will help you end up in more inboxes and avoid spam folders.

How is deliverability measured? Many factors influence email deliverability. Generally, three questions are asked by mailbox providers (such as Yahoo, Google, Outlook, etc.) to determine what inbox an email ends up in.

  • Is this message safe?
  • Is it wanted by most Subscribers?
  • Is the message wanted by this specific person?

If YES is the answer to all 3 questions, the email will most likely end up in the inbox. Otherwise, it will end up in spam.


What is your sender's reputation? Mailbox providers rely on your sender's reputation to create a ‘sender score’ using algorithms. There is not a one-size-fits-all approach to this, so each provider keeps their specific calculation and algorithms private, but one critical factor is how subscribers engage (or fail to engage) with your messages. How your subscribers interact with your mail is known as subscriber engagement. Their engagement with you can be positively or negatively impacted by subscriber behaviors. Here are a few tips for promoting positive subscriber engagement:


Subscriber List Health

  • Focus on quality vs. quantity. Use subscribers who have given you explicit permission to communicate with them.
  • Use a double opt-in or ReCaptcha for form security to prevent bot usage.
  • Clean or scrub your list frequently of cold subscribers. Having a growing list of unengaged subscribers will drop your reputation as those emails start filtering to subscribers’ spam folders.



  • Try not to make sudden, drastic changes to the way you send messages, as mailbox providers will view these messages as risky, likely filtering them to spam.
  • Using multiple domains is okay, but be sure they are recognizable and have been active within the last 6 months.
  • Volume: send communications to a consistent number of subscribers.
    • NOTE: it is normal for your list to grow or shrink, but try to not have any major swings (don’t jump from 2,000 subscribers one day to 10,000 overnight).
    • If you have a large influx of subscribers, divide them into batches to slowly grow your database.
  • Frequency: Maintain your reputation by ending at least one email per month. If you go ‘dark’ for too long, your reputation won’t be maintained and you’ll essentially be starting from scratch with your next email. Contrarily, don’t send emails too frequently as it could be flagged as spam.
    • NOTE: it is highly recommended to give your subscribers the option to determine how often they want to hear from you.


  • Content influences your deliverability as an underlying data point, especially if you don’t have a good consistency. If you send inconsistently, the actual content can be used to determine the safety and subscribers’ desire for your content. If you do send consistently, then content is often ignored.
  • Don’t use spammy words/phrases or gimmicks. Try to make your email sound more conversational and human, even if you’re selling something. Don’t make it sound too urgent or overly promotional. Don’t use “tricky” subject likes like “RE: Your Order #12345” 
  • Eliminate link shorteners: these are often used by spammers, and some spam filters may automatically red-flag these. Use the direct, full links for transparency.
  • Focus on your image-to-text ratio. While there isn’t a magic recipe here, the best practice is to have enough text, so if an image fails to load, the text will still effectively communicate your message.
  • Drive authentic engagement: encourage subscribers to engage authentically. Maybe ask them to reply to your message with their favorite show they’re currently binge-watching, their favorite song, or a great recipe they’ve recently cooked.

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