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Five Causes of Poor Email Deliverability


One out of every five commercial emails never reaches the inbox. So where do they go? They can be delivered to junk, spam, or even go missing. Getting emails delivered to the inbox involves more than just hitting send.

Deliverability Matters

Deliverability is key to a successful email marketing program. After all, subscribers can’t engage with emails they never see. At Return Path, we study global inbox placement rates so we can help our clients improve their sender reputation, subscriber engagement, and ultimately their email deliverability. We’ll help you reach the right inbox and increase your email ROI by getting more email delivered to more of your subscribers.

How do you know if you have a deliverability problem?

  • You’re experiencing a drop in engagement rates like opens and clicks.
  • You see an increase in email bounces.
  • You’re being blocked at a mailbox provider.

The deliverability landscape is changing, and it’s only getting harder to reach your subscribers’ inboxes. Inbox placement and deliverability impacts the success or failure of your email marketing program, and ultimately your email return on investment.

Five Causes of Poor Email Deliverability

  1. Negative Sender Reputation: Maintaining a positive sender reputation is vital to the success of your email program. Sender reputation is an indication of the trustworthiness of an email sender’s IP address and sending domain. Mailbox providers take various metrics into consideration to determine your sender reputation, including spam complaints, mailing to unknown users, industry blacklists, and more. Find out your sender reputation at
  2. High Complaint Rates: The key to email marketing is to ensure you are sending relevant and timely emails to people who want to receive them. If you aren’t, then you are opening yourself up for subscriber complaints. And the more complaints you receive, the worse your email deliverability can become. Keeping your subscriber complaint rate low is crucial to maintaining a positive sender reputation and high deliverability rates. Learn more about why and how subscribers complain, and how to improve your complaint rates with A Marketer’s Guide to Subscriber Complaints.
  3. Getting Listed on a Blacklist: In the world of email, there are whitelists, greylists, and – of course – the dreaded blacklists. A blacklist is a list of domains and/or IP addresses that have been reported to be “known” sources of spam. They are available to the public and exist to help mailbox providers protect their users from unwanted email. If your practices or your content look spammy, you could wind up being blacklisted, regardless of whether or not you’re a legitimate, permission-based sender. Find out if your IP is blacklisted with our free tool.
  4. Poor List Quality: Maintaining a high quality subscriber list is imperative to ensuring your emails are delivered to the inbox instead of the junk or spam folder. In addition to complaints, there are three other major culprits of poor list quality: spam traps, unknown users, and inactive users.
    • Spam traps are email addresses that don’t belong to active users and are used to identify both spammers and senders with poor data quality practices.
    • An unknown user is a recipient that never existed, has been terminated by the mailbox provider, or was abandoned by the end user.
    • Inactive addresses represent customers on your list file who have not opened, clicked, or taken some kind of action for a significant amount of time. Learn more about how to identify inactive subscribers, as well as how to improve your overall list quality with The Ultimate Guide to Email Deliverability.
  5. Lack of Email Authentication: Authentication allows the receiver of an email and the mailbox provider to confirm the identity of the sender. If the identity of the sender cannot be authenticated,  mailbox providers may reject the message or put it through additional filters to determine whether it should be delivered. Read our blog post, “Authentication 101: The Fundamentals,” to learn more and understand why authentication is important.
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Experts in Deliverability

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