Email Marketing

Email Deliverability

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Email deliverability refers to the number of emails delivered to the subscriber’s inbox. This key metric helps marketers understand the efficacy of their email program and whether they are maximizing brand visibility to drive conversions.

Email deliverability should not be confused with emails delivered. Delivered refers to emails that were successfully accepted by the mailbox provider (MBP). It does not represent the rate or number of emails placed in the inbox or spam folder. An email program may appear successful if 97% of emails were delivered, but in reality, these emails may have landed primarily in the spam folder. Monitoring your delivered rate is important but knowing your inbox placement rate will help provide insight into the health of your email program.

Discover how Everest provides visibility into your inbox placement rate so you can accurately measure email performance and resolve issues preventing you from reaching your subscribers.

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How does email work

Email isn’t as simple as clicking “Send”. Rather, it’s a multi-step process with numerous layers and a gauntlet of checks.

When a sender creates and deploys an email (typically through their email service provider, or ESP), it is transferred from server to server via the Simple Transfer Mail Protocol (SMTP). To determine the destination email address, the SMTP contacts the DNS server and checks whether that domain has any mail exchange servers with information about where the message should be sent.

Once the SMTP has confirmed the destination, it transfers the message to the email recipient’s Mail Transfer Agent (MTA) server, commonly hosted by an Internet Service Provider (ISP, also known as a mailbox provider, or MBP) such as Gmail, Microsoft, and Yahoo. Before the email reaches the ISPs’ server, additional checks are run on the sender’s authentication, IP and Domain reputation, and infrastructure to ensure they are safe and can be trusted.
Once the email has successfully made it through the MBP’s gateway, it is considered delivered. The sender’s reputation and subscriber engagement history will determine whether the mail will land in the inbox or spam folder. The inbox placement rate is based on the number of messages that reached the inbox.

~20% of sent mail is not reaching recipients’ inboxes.

A high inbox placement rate is determined by the health of an email program. This health relies on adherence to email best practices like list hygiene, content evaluation, and engagement, but infrastructure and authentication also play a significant role in an email program’s success


Learn more about email deliverability, what affects your deliverability, and how your deliverability impacts your email performance.

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Infrastructure refers to the hardware and software used to deploy emails, including the Domain Name System (DNS) and authentication. Think of the DNS as the internet’s phone book – it links hostnames (the domain name) to specific IP addresses so emails know exactly where to go. The DNS record also holds authentication records such as DKIM, SPF, and DMARC. This helps verify that the sender is authorized and deploying legitimate mail. Mail servers will perform checks to confirm that a sender is allowed to send and receive based on their DNS record. If there is no record present, emails are less likely to be delivered.
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Email authentication

Email authentication is critical in identifying and addressing spoofed messages in order to protect the end subscriber from malicious attacks. Authentication refers to techniques that provide verifiable evidence that an email originates from a legitimate source. It is email’s way of proving the message comes from who it claims to come from by validating domain ownership. The following authentication protocols are the top three ways to avoid spoofing attacks:
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Sender Policy Framework (SPF)

SPF records list which IP addresses are authorized to send email on behalf of domains. The SPF record helps MBPs and filtering systems recognize the difference between forged and legitimate email. SPF checks are run based on the path the email took to get from its origin to its destination.
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DomainKeys Identified Mail (DKIM)

DKIM is an authentication protocol that adds a digital signature to every sent email message. The signature is a header added to the message and secured with encryption. MBPs and receiving servers use DKIM to determine whether the message was changed or altered during transit. When a message has been signed using DKIM, MBPs that successfully validate the signature can use information about the signer as part of a protection from spoofing and phishing.
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Domain-based Message Authentication, Reporting & Conformance (DMARC)

DMARC addresses exact-domain spoofing and phishing attacks by preventing unauthorized use of a domain in the “From” address of email messages. DMARC is quite different from the other authentication methods. It is a framework that sits atop SPF and DKIM authentication, rather than working in silo alongside it. DMARC allows the sender to specify how unauthenticated or non-compliant messages should be treated by MBPs. It helps mail administrators prevent hackers and other attackers from spoofing their organization and domain.

The true beauty of DMARC protection lies in the three available policies which allow senders to instruct the MBPs on how to treat unauthenticated mail. The three options are:

  • Policy is ‘none’ (p=none): MBPs will take no action and deliver the mail as normal
  • Policy is ‘quarantine’ (p=quarantine): MBPs will send the message to spam/junk
  • Policy is ‘reject’ (p=reject): MBPs will drop the message and it will not be delivered to recipients
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Email deliverability best practices

In addition to a correctly configured infrastructure and authentication record, following general email best practices will help boost email deliverability. Email best practices should be followed by all marketers since they help maintain a strong sender reputation. This is something MBPs consider when determining whether to let the email get past the gateway and whether the message should land in the inbox or spam folder.
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Sender reputation

Sender reputation is how MBPs measure the trustworthiness of an email program. MBPs use sender reputation to determine if emails should be delivered to the inbox, the spam folder, or blocked completely. A poor sender reputation results in fewer emails delivered to your subscribers’ inbox, which can reduce conversions and, ultimately, ROI. There are two key factors of sender reputation:

  • Engagement: Engagement describes subscriber activity with email, which may be positive or negative.
  • Positive engagement includes rescuing email from the spam folder or marking it as not junk, opening or clicking on the email, or moving the message into a folder.
  • Negative engagement includes actions like marking the email as spam or junk (also referred to as a spam complaint, and the number one reason for declining sender reputation), deleting the email without opening, or never reading the email at all.
  • List hygiene: Sending to bad email addresses indicates that a sender is employing risky acquisition practices and isn’t sending to subscribers who signed up to receive their emails
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List hygiene

List hygiene is a process of data validation undertaken by email marketing teams to ensure that they have a clean email list comprised of valid and positively engaged subscribers. A successful email program is closely tied to having healthy email lists, as list hygiene is a top priority for MBPs. There are three types of bad email addresses to avoid in order to maintain a clean email list:

  • Unknown users: Unknown users are invalid or unrecognized email addresses in a sender’s database. Examples of unknown users include email addresses that have been abandoned and shut down by the MBP, or email addresses that have been mistyped or malformed and are therefore not actual email addresses.
  • Recycled spam traps: Recycled spam traps, sometimes called repurposed spam traps, are addresses that were at one time legitimate destination addresses that have been repurposed to catch abusive mail.
  • Pristine spam traps: Pristine spam traps, also referred to as true traps or honeypots, are email addresses created solely to capture spammers. These email addresses were never used as legitimate email addresses, do not subscribe to email programs, and do not make purchases.

Sending to these types of email addresses negatively impacts sender reputation and the chances of an email making it past the gateway and into the inbox. Blocklists, which also contribute to a sender’s reputation, monitor spam trap activity to catch any senders that have poor email address acquisition practices.

Discover how Validity BriteVerify can help keep your email lists clean to protect your sender reputation.

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Schedule and consistency

It is common for malicious senders to use an IP address with no existing volume or reputation history to send as much mail as possible over a short period of time — before the MBP or ISP filters can catch and block the traffic. As a result, MBPs prefer consistent volume to help measure sender reputation. Large email sends should be throttled over multiple days to avoid volume spikes, which can trigger MBP filters.
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Segmentation and personalization

The days of batch and blast emails are long over. Segmented email campaigns that include personalized details specific to the subscriber have much higher conversion rates. While first name personalization has grown in popularity, adding personalized content based on the subscriber’s interest will more effectively resonate with the subscriber.
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Brand recognition

Brand recognition is as important as personalization and segmentation in helping senders stand out in the inbox leading to higher open rates. Ensure branding remains consistent across all platforms— from the website to social media — to help build and maintain a relationship between the brand and the subscriber.

“We are clear there’s a straight-line relationship between better inbox placement performance and Philips’ program revenue. We also now have a deep understanding of what affects our deliverability and why, which has improved our engagement levels significantly.”

– Charlie Wijen – Digital and CRM Specialist, Philips

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Email deliverability is a complex web of processes that determines whether an email will land in the inbox or spam folder. Successful deliverability relies on technical elements like sound infrastructure and correctly configured authentication settings, as well as subscriber-facing elements like brand recognition and campaign frequency. It’s important to monitor your sender reputation and inbox placement rates to uncover both vulnerabilities and areas of opportunity for your email program.

Schedule a free demonstration to see how Validity can improve your sender reputation so you get get more messages to more people.



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