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How Email Deliverability Works

If you’re sending out marketing emails, you’re probably tracking all the important stats, like your open rate, click rate, and the number of people who unsubscribe. But email deliverability is often overlooked, even though it is essential in order to get results from your emails. In this article, we’ll provide an introduction to email deliverability and explain how email servers test emails before they reach your inbox.

To read more on Growthlabs’ experience with Email Marketing, visit here.

What is Email Deliverability?

When sending an email to one or more recipients, you tend to assume that it will successfully reach them, but that isn’t always the case. Email deliverability can be defined as the likelihood of an email arriving in the intended inbox.

It’s one of the most frustrating problems people experience when dabbling in email marketing. Imagine this; you spend hours crafting the perfect email and pulling together the list of relevant contacts, only to find that 30% of the intended recipients didn’t receive the email.

“Why wasn’t my email delivered?”

Many email service providers will analyse your email and prevent it from reaching an inbox if issues are identified. The server will return a report to you highlighting that there was a problem with what you sent. However, the answer to the question, “why wasn’t my email delivered?”, often isn’t clear cut and it can be tough to figure out what to do next.

Common reasons your email wasn’t delivered:

  • Email providers are marking the email as spam
  • The email address is invalid
  • It went to a junk folder
  • The mail server blocked the email
  • Your mail server has been blacklisted

Non-delivered emails are typically referred as ‘bounced’, and classify as any email that falls into the above category. When sending mass emails – such as in a targeted campaign – you want to be careful to avoid sending a campaign wherein the bounce rate is higher than 2%, as this highlights an unsuitable mailing list, and can potentially lead to your account being flagged by the email provider.

Email Authentication

The purpose of email authentication is to safeguard recipients from spam emails and emails that could be malicious. As a result, email deliverability is also determined by the authentication process. SPF, DKIM and DMARC are crucial areas of email authentication which we will break down for you.

With the threat of email phishing remaining high as ever, email authentication is a vital resource that can be used to protect your business from potential scams – in 2021, it was estimated that 283 BILLION spam emails were being sent a day worldwide.

Sender Policy Framework (SPF)

SPF is a technique designed to prevent spammers from sending emails using your domain. You can integrate an SPF record into the Domain Name System (DNS) settings, specifying which IP addresses and hostnames are permitted to use your domain to send out emails. By implementing SPF, any unauthorised emails will be marked as suspicious and rejected, preventing them from reaching your company’s inboxes.

SPF is, by far, the most commonly used email deliverability protocol – a 2022 study concluded that over 30% of email domains were deploying an SPF record.

DomainKeys Identified Mail (DKIM)

DKIM is an email security standard which was designed to ensure that emails do not change between the time that they are sent and when it arrives in the destined mailbox. DKIM uses “public key cryptography” to validate that an email came from a trustworthy mail server.

Putting it simply, the email is signed with a private key when it’s sent, and then a public key attached to the domain’s DNS is used by the receiver’s server to verify that the email hasn’t been forged. DKIM also confirms that content within the email hasn’t been altered during its journey to the inbox. Sending emails with DKIM signatures are deemed to be safer and more legitimate, meaning your email deliverability will be higher.

DKIM is a highly secure measure, supported by domains as high as the British Government.

Domain-based Message Authentication Reporting and Conformance (DMARC)

DMARC is another email authentication protocol which is designed to give email domain owners the ability to prevent people from using their domain without their knowledge. DMARC safeguards businesses against email scams, phishing emails and other cybersecurity threats that are becoming more common.

The domain owner will create instructions within the DNS settings which the email server will use to authenticate all emails that try to reach a specified inbox. DMARC is an extension of DKIM and SPF, which means it combines the functionality of both, helping it to perform a thorough check of an incoming email.

Often used as a means of preventing malicious threats from manipulating their brand’s domain, DMARC is a highly recommended protocol to deploy from a business perspective – 88% of users believe they are likely to trust a brand deploying such secure protocols.


We know that was a lot to take in at once, so here’s a quick summary:

  • SPF authentication provides email senders with the ability to define which IP addresses can send emails from a specific domain.
  • DKIM uses an encryption key and signature to ensure emails have not been altered in any way.
  • DMARC uses both forms of authentication to prevent cyber threats and unauthorised use of its domain.

As a digital marketing agency, we’ve been running email campaigns for years, learning from experience how to enhance email deliverability. If you’d like to level up your email campaigns, consider outsourcing them to us.

As specialists in email marketing, we know how to create compelling subject lines that drive clicks, and clever content that encourages conversions. Your emails will drive much better results with us managing them, making the switch a smart investment.

If you’d like to outsource your email marketing and enhance your deliverability, get in touch.