According to Return Path’s 2018 Deliverability Benchmark Report, 15% of emails around the world fail to reach subscriber inboxes.

And it doesn’t just encompass spammy content. It includes emails such as newsletters and shipping notifications, emails that subscribers actually want to receive. Unsuccessful email deliverability isn’t just a missed phone call. It can negatively impact your relationship with customers over time.

This comprehensive guide will help you understand what it is, why it’s important, what affects it, and what you can do to improve email deliverability overall.

What is email deliverability?

Email deliverability is when an email successfully arrives into a recipient’s inbox. Which is not to be confused with email delivery, which simply means that an email has been successfully delivered to the recipient’s server.

  It’s possible to have stellar email delivery and poor email deliverability at the same time, it’s just that all your emails are landing in spam folders instead of inboxes .

What affects email deliverability?

1. Your sender reputation

Sender reputation, a score that an Internet Service Provider (ISP) assigns to any company that sends out emails, is integral to figuring out how to increase deliverability.

It’s fairly straightforward – the higher your score, the more likely your email will land in your customer’s inbox. Maintaining sender reputation is important, as if scores fall below a certain level, ISPs will either reject emails or send them to spam folders.

Sender reputation is affected by:

  • The number of emails sent by the company
  • The number of spam-marked emails or recipient complaints
  • The number of times emails from the company hit the ISP’s spam trap
  • The blacklists that the company has been added on
  • The number of bounced emails from the company
  • How many recipients are opening (or not opening), replying to, forwarding, and deleting emails from the company, and whether they are clicking on the links within the email
  • The number of unsubscribed emails

2. Subscriber engagement

Subscriber engagement is essential to successful email deliverability since it has a direct impact on sender reputation. ISPs are always keeping an eye on how your subscribers are engaging with your emails. Are they interacting with your emails positively, or are they complaining about you?

If subscriber engagement is positive, then ISPs will route your emails to inboxes. If subscribe engagement is negative, then you’re likely to be receiving complaints – which hurts deliverability.

A couple tips to improving subscriber engagement:

  • Keep in mind that the quality of content and design goes a long way.
  • You should sunset disengaged customers by filtering them out of your list if they have not opened an email for a period of time.


3. New IP or domain

What you might not realize, when changing to a new email service provider, is that it essentially resets the sender reputation that you’ve been lovingly nurturing.

As sender reputations are tracked against your IP address, shifting to a new one means that you’ll have to build from scratch again. When reincarnating an IP or domain:

  • Do a list clean up of all your unsubscribes, complaints, or bounces before importing it over. Including these emails in your new list can immediately ruin your sender reputation
  • Give ISPs time to monitor the behavior of your new address and how your audience is reacting to it by slowly ramping up your email frequency
  • Run a content campaign to raise awareness on your new address, such as a re-introduction email that informs customers of your new domain. This is so your audience doesn’t get confused and react with low or negative engagement. However, this step is only necessary if you changed your domain or the corresponding “from” email address.

Like a newborn, carefully nurture the early life of your new domain and ensure bounce and complaint rates are low.

4. List quality

List quality also greatly impacts deliverability, which is why it’s important to consistently monitor and prune your email lists.

Two elements effect your list quality:

  • Presence of spam traps
  • Frequency of bounces

What are spam traps?

There are two different types of spam traps.

The first kind are “pristine” spam traps, fraud management tools used by ISPs to identify spammers. They look like real email addresses, except they don’t belong to anyone and so they’re unable to opt-in to email lists.

These spam trap addresses are placed on web where people, or robots harvesting emails, illegally obtain them.

The second type are “recycled” spam traps – which are old, inactive emails. They typically spend some time as an “unknown user” before the email provider re-purposes them into a spam trap.


What are bounces?

Hard bounce

The email was completely undeliverable, and delivery shouldn’t be attempted again in the future. It happens for one of three reasons:

  • Email address or recipient doesn’t exist
  • Email domain doesn’t exist
  • The recipient’s server has blocked delivery

Soft bounce

A soft bounce is salvageable because it just indicates a temporary issue. Your email provider will usually attempt delivery to an address over a few days before officially marking it as a soft bounce. It happens for a few reasons:

  • The recipient’s inbox or server is full
  • The target server is down
  • Your email might be too large to deliver

How to improve deliverability

Now you know the factors that are getting in the way of your email deliverability, what are the things you can do to ensure the safe passage of your emails?

1. Authentication

Authenticated emails are a key part to email deliverability. It basically communicates to the server whether your email is from a legitimate source, and it also determines the authenticity of your domain.

To understand this further, you have to know a few acronyms that you’ll see in your email deliverability research.

DMARC: Stands for Domain-based Message Authentication, Reporting, and Conformance. It’s a technical standard that is in place to protect both senders and recipients from spam, spoofing, and phishing.

SPF: Stands for Sender Policy Framework. It’s an email authentication technique that works by detecting forgery and spam. It works similarly to DMARC, which shows the subscribers’ servers that they’re a legitimate sender.

DKIM: Stands for DomainKeys Identified Mail. It’s another email authentication protocol that lets companies verify that messages were sent from authorized servers by using “public key cryptography”. It also protects against forgery and spam.

MX Records: Stands for “mail exchange” records. They are used to communicate which mail servers can accept incoming mail on behalf of a domain, and also where the emails should be routed to.

If your MX records aren’t configured to the right location, you won’t receive any emails. The emails you send may also be rejected as this is an important part of validating your sender domain.

2. Opt In

The most popular form of opting in is the single opt-in, which is a subscription method that requires a single action. While this may seem like the best way to grow your email list, single opt-in strategies are typically inconsistent, which can lead to a lot of spam complaints.

For example, some single opt-in forms come with the checkbox already filled in, which means the subscriber did not actively give their consent.


Spam complaints can be the kryptonite to your email program. Just a few spam reports (per 1,000 emails) can lead you to being blocked.

To ward off complaints, the best thing you can do is use double opt-in, which encompasses a confirmation email to new subscribers in order to gain consent.

3. Create a clear unsubscribe process

While it may seem counterintuitive to make it easy for your subscribers to leave, there can be few things more damaging to your brand than a hidden or difficult unsubscribe process.

As some email marketers will hide unsubscribe links or require a lot of hoop jumping before the subscriber can effectively leave. Parting words of “we’re sad to see you go, but hope we can work together in the future” vs. repeatedly prompting “are you sure you want to unsubscribe,” will leave a much better impression.

Fact is, if someone wants to unsubscribe to your content, they’ll find a way, and it’s best that it’s not by ways of a complaint.

Another way to minimize complaints is to add a List-Unsubscribe header to your emails. It’s basically optional text you can add to the header of your emails that allows subscribers to effortlessly unsubscribe. List-Unsubscribe headers are useful for two reasons:

  • ISPs and spam filters view these headers favorably
  • Subscribers will have a more positive experience with your brand

4. Whitelisting

Whitelisting is basically adding an email to your list of contacts, which communicates to inbox filters that this address is a trusted source. It’s possible to ask subscribers to whitelist you, which will help to improve email deliverability.

An ideal way to get whitelisted is to link to a set of instructions in your email campaign.

It can sound something like like this: You’re receiving this email because you opted in through our website. Make sure these emails keep coming.


Remember, a request to be whitelisted is a tall order, so make sure you’re reserving it only for your most loyal of subscribers.

5. Consider email frequency

To improve email deliverability, it’s best to avoid annoying your subscribers by sending too many emails. As it turns out, there’s a sweet spot when it comes to the frequency of emails that you send out.

While data points to once every two weeks as the ideal send frequency, it’s by no means a science. So to determine the ideal email cadence, which is the timing and types of emails you send out to your subscribers, you can try the following tips:

  • Know who your audience is and understand their customer journey
  • Survey your audience to learn how to segment your list accordingly
  • Set up an email preference center to give your subscribers more control


6. Avoid using spam words

Inbox filters are the seemingly omniscient blockers to your email programs. And they’re especially sensitive to spam trigger words that will re-route your well-intended emails away from the inbox.

Avoiding using spam trigger words such as these might help your email deliverability cause, and there’s also a few things you can avoid:

  • Avoid using all caps, exclamation points, and red fonts
  • Use a reliable email service provider
  • Don’t attach files to your emails


Learning how to increase deliverability is a long road, and it’s a strategy that you’ll need to be constantly refining in order to deliver valuable email content to your subscribers.

You can monitor the health of your email deliverability with the following tools:

  • Litmus spam checker: A spam checker tool that scans your email across major spam filters before you hit send
  • Gmail Postmaster Tools: For companies that send a high volume of emails out (to Gmail users specifically) to find out if users are marking their emails as spam, if emails are being sent securely and according to Gmail best practices
  • A tool to help you monitor your sender reputation score.

Email deliverability: What is it and how to improve it

 To increase deliverability, reduce surprises. Stick to the same “From” text, same day of sending, same time of the day. The more recognizable and expected your email is, the higher the chance it will be opened. The more people open it, the more trusted you are and your deliverability will improve.