What is email deliverability rate?

Your email deliverability rate is a measurement of how many of the emails you send actually get delivered to the intended recipients’ inboxes. It’s also referred to as an acceptance rate or an email success rate.

Email deliverability is expressed as a percentage, and you can work it out by dividing the number of emails delivered by the number that was sent. Depending on your Email Service Provider, this metric should be easily found from your dashboard or campaign analytics section.


It’s not to be confused with bounce or “delivery” rate, which is a measurement of emails that could not be delivered in the first place and are returned to you. This is due to a number of factors, including but not limited to an inaccurate email address, lack of permission (ie. the recipient is not opted-in to receive emails from you or has blocked you) or the recipient’s inbox is full. 


When an email cannot be delivered, it’s because the email server (e.g. Google/Gmail or Microsoft/Outlook) has stopped it, is experiencing an issue or simply doesn’t exist. Where the failure is potentially “temporary”, we would retry for a period of 72 hours (giving the server time to resolve an issue on their side) before it is considered undeliverable.

What is a good email deliverability rate?

Naturally, you want 100% of the emails you send to be delivered. That’s not possible to guarantee, but there’s no reason why you shouldn’t be close to that goal.


Once your deliverability rate has sunk and/or your sender reputation has been compromised then it can be very challenging to repair the damage. That’s why maintaining an exemplary record in the eyes of the servers is vital. 


It is possible, however, provided you take the necessary steps.

Why are my emails not being delivered?

To put it simply, your emails are not being delivered because the recipients’ email clients suspect you are sending spam.

With billions of emails being sent every day, they need to be vigilant. 

Take a look at the graph below, which charts the estimated volume of email traffic that is considered spam. Clearly, ISPs and the likes of Gmail have been doing a pretty good job over the last 6 or so years!


Unfortunately, an “honest actor” may be penalised unfairly, but these cases are rare. You may feel that your brand is one of these.

However, it’s likely that you’ve unintentionally done something to negatively impact your sender reputation.

Some common causes would be;

  • Sending to old, “stale” lists

If you have an email list that you haven’t been in contact with for a long period of time (~1 year) which you have started sending to again recently then that may have triggered a spam alert. We advise brands regularly “clean” their lists to avoid this.

One way of doing this is to simply segment your lists based on how recently they signed up (within the past 6 months, let’s say) and when they last opened an email from you. This way, likely non-openers are continually filtered out.

  • Very low engagement rates

If your emails are going unread a lot of the time then this would indicate to the email client that they are unwanted. Improving your subject lines through personalisation, and segmenting your audience to keep the content relevant, will help you to increase your open and click-through rates.

  • A sudden and dramatic increase in the volume being sent

It might seem odd that you’d be penalised for sending a high volume of emails, but it can happen if you go from sending 100,000 let’s say, to 200,000 in the next campaign.

The implication, unfortunately, is that you’ve done something underhanded to grow your list so quickly. Again, if we look at this from the perspective of preventing spam, there is still a certain amount of “list buying” that goes on. And that’s what the email client will suspect has happened.

Even if you are growing your email list the right way, getting clear consent through ethical practices, you still need to gradually increase your email volume for bulk campaigns.

  • Too many campaigns

The frequency of your email campaigns is another important factor to consider. In general, send no more than 2-3 per week. Of course, there are exceptions and brands can still execute once-a-day campaigns without a penalty. 

So what gives? The issue isn’t the frequency per se, it’s more a case that if you are constantly emailing someone then you do increase the risk of them unsubscribing. A large number of unsubscribes would be another red-flag to the server.

If sending multiple email campaigns per week is an integral part of your strategy then you need to make sure that 1) you are personalising the content to maximise engagement rate and 2) you have imposed a frequency cap to ensure that individual recipients are not over-messaged. 

Key Email Deliverability Rate Terms Explained

  • Sender Reputation

This is a measurement of how trustworthy the various email clients perceive your IP address. A number of factors contribute to this rating, but essentially it’s to do with triggering their spam trap or if you’ve been blacklisted outright at some point.

Check your reputation here at BarracudaCentral.

  • IP Address

This is considered the official source of the emails. Commonly, your Email Service Provider will provide a dedicated IP address for you. This needs to be “warmed up” (gradually building the send volume) to earn the trust of the email servers.

  • Email Blacklist

This is a real-time list kept by various internet service providers, email clients and so on, which documents any IP address that is known to send spam. You can end up on a blacklist for numerous reasons, like if enough people report your email as unwanted, or your list of recipients significantly increases within a short period of time (as mentioned, a potential sign you’ve done something untoward!)

What can I do to improve my deliverability rate?

We understand that a poor email success rate is at best a very frustrating thing to experience and at worst has a hugely detrimental effect on your brand’s revenue.

It’s one of the main reasons why brands switch email service providers, alongside better functionality, capabilities and support. 

Bearing in mind our early point about the difficulty in repairing your reputation, here are some of the things you can do as a marketer to ensure your emails hit their mark more often.

  • Better email list hygiene

Clean your lists regularly, at least once every 3-4 months. Remove unengaged email addresses, if they haven’t opened an email in the past 6 months then it’s either a dormant account or they are simply not interested in hearing from you.

  • Always get permission

Email is a permission-based channel; you can’t send someone a commercial email unless they have given you permission to do so. It’s worth thinking about using the double-opt-in method too, as then you can be sure that list only contains people who are genuinely happy to receive emails from you.

  • Better customer segmentation

If every email you send goes out to everyone on your list then there’s something wrong. It means that you aren’t sending content based on the different interests of the recipients and aren’t tailoring your messaging to reflect their stage in the customer lifecycle.

Segmentation doesn’t need to be complicated, and you can start simply by grouping customers together based on behaviours like “date since last purchase”, “recently viewed sportswear”, or create a list of highly-engaged customers based on how frequently they read your emails.

Technical ways to improve your email deliverability

The above tactics are very much “customer-facing” improvements, but they don’t always get to the heart of the problem which is how to persuade Gmail, Hotmail and everyone else that you are who claim to be and are to be trusted.

That’s where email authentication comes into play.

How to get your emails authenticated

There are a couple of key components to this, which work as a sort of one-two punch to safeguard your email deliverability rate. They are considered essential and it is paramount that they are set up correctly.

  • Sender Policy Framework (SPF)

An SPF is a way of verifying that the IP address sending the email has the authority to do so from the domain it claims to be. It’s basically a list of approved IP addresses that is submitted to the recipient’s server. This is something that is managed exclusively by the Email Service Provider, so the client doesn’t need to consider it.

  • DomainKeys Identified Mail (DKIM)
Again this is to do with proving your identity and authority. DKIM is a way of encrypting your emails with a unique and private key that only you have. The recipient’s server is then given a public key that can be used to decrypt it upon arrival. DKIM is the number one thing you can do to safeguard your sender reputation.

Wrapping up

If you simply can’t afford to take a risk with your email deliverability rate (and let’s face it, who can?) then get in touch with us and we can advise you in more detail on what to do.

We are vastly experienced in this field, working with hundreds of leading brands to deliver personalised email campaigns at scale. We operate to the highest industry standards, ensuring consistently high deliverability rates for all of our clients.