What is Email Deliverability, DMARC, DKIM, and SPF?

In the fast-paced world of email marketing, achieving successful email deliverability is paramount. It's not just about composing compelling messages; it's about ensuring they land in your recipient's inboxes. 

To help you make the most of your email marketing efforts, we'll dive into the fundamentals of email deliverability and its core components: DMARC, DKIM, and SPF. 

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What is Email Deliverability?

Email deliverability refers to the ability of an email message to reach its intended recipient's inbox without being marked as spam, bounced, or otherwise obstructed. Essentially, it's a measure of your email campaign's success in navigating various filters and hurdles set by email service providers (ESPs) and internet service providers (ISPs). High deliverability rates are synonymous with effective communication, while poor deliverability can hinder your marketing efforts significantly.

A 1% increase in email deliverability can result in a 10% increase in email open rates and click-through rates.

From the sender's perspective, achieving optimal deliverability involves understanding the factors influencing inbox placement. Key elements include sender reputation, content quality, list hygiene, authentication protocols like DMARC, DKIM, and SPF, and avoiding spammy practices. It's important to remember that deliverability isn't solely reliant on your content or email platform; it's a complex interplay of various factors.

The repercussions of poor deliverability can be substantial. When your emails consistently end up in spam folders or get blocked, you miss out on valuable opportunities to engage with your audience. This not only affects your marketing ROI but can also tarnish your brand's reputation. On the other hand, high deliverability rates lead to improved open rates, click-through rates, and, ultimately, conversion rates.

Metrics to Measure Deliverability Success

Measuring email deliverability success involves tracking several critical metrics, including:

  • Bounce rate: The percentage of emails that couldn't be delivered.

  • Open rate: The percentage of delivered emails that recipients opened.

  • Click-through rate (CTR): The percentage of recipients who clicked on a link within your email.

  • Spam complaint rate: The number of recipients who marked your email as spam.

  • Unsubscribe rate: The percentage of recipients who opted out of your email list.

  • Sender score: A numerical assessment of your sending reputation.

By monitoring these metrics, you can gain valuable insights into the health of your email deliverability and make data-driven improvements to your campaigns.

What is DMARC?

DMARC, or Domain-based Message Authentication, is a vital authentication protocol in the world of email marketing. It's a robust email authentication protocol that empowers senders to protect their domains from email phishing and spoofing attacks. It adds an extra layer of security by aligning two other important authentication mechanisms (SPF and DKIM) and instructs receiving email servers on how to handle messages that fail these checks.

DMARC allows senders to publish a DMARC policy in their DNS (Domain Name System) records. This policy outlines the sender's instructions on what receiving email servers should do when an email fails SPF and/or DKIM authentication checks. There are three possible DMARC policy actions:

  • None: This action is essentially an observation mode. It enables senders to monitor email authentication failures without impacting email delivery. It's a valuable starting point to understand the scope of the problem.

  • Quarantine: In this mode, emails that fail authentication checks may be placed in the recipient's spam or quarantine folder, ensuring they don't reach the inbox.

  • Reject: The most stringent action, "reject," instructs receiving servers to reject any email that fails DMARC authentication. This ensures that only authenticated emails from authorized senders reach the inbox.

The advantages of implementing DMARC are numerous:

  • Enhanced deliverability: DMARC significantly boosts email deliverability by reducing the likelihood of emails being classified as spam or phishing attempts.

  • Brand protection: Safeguards your brand's reputation by preventing cyber criminals from impersonating your domain in phishing attacks.

  • Data security: By ensuring that only legitimate emails are delivered, DMARC helps protect sensitive information and customer data.

  • Visibility and reporting: DMARC provides valuable insights into your email traffic. You can receive reports on authentication failures, helping you fine-tune your email security measures.

Setting up DMARC involves a series of steps:

  • Domain check: Identify the domains you want to protect with DMARC. Review your domain's DNS records to ensure they're correct.

  • Policy decision: Decide on your DMARC policy: none, quarantine, or reject. Create a DMARC record with this policy and alignment rules for SPF and DKIM.

  • Publish DMARC records: Add the DMARC record to your domain's DNS settings for email servers to find and follow.

  • Monitor and adjust: Configure DMARC to send reports to your email for monitoring. Analyze these reports regularly to improve your DMARC policy. Start with a "none" policy for observation and gradually tighten security as needed.

By understanding DMARC and its role in email authentication, you're taking a significant step toward improving your email deliverability and securing your brand's online presence. 

What is DKIM?

DKIM (DomainKeys Identified Mail) is an email authentication method that adds a digital signature to your outgoing messages. This signature is generated using a private key, and it provides a way for receiving email servers to verify that an email originated from the domain it claims to be from. In essence, DKIM acts as a seal of authenticity for your emails.

Here's how DKIM works to ensure message integrity:

  • Signing: When you send an email, your email server uses a private key to create a unique digital signature for that message. This signature is embedded in the email's header.

  • Verification: When the receiving email server receives your email, it checks the DKIM signature against the public key published in your domain's DNS records. If the signature matches, the email is considered authentic; if not, it's a sign of potential tampering or forgery.

  • Authentication result: Based on the DKIM verification, the receiving server assigns a DKIM "pass" or "fail" status to the email. It's more likely to be delivered to the recipient's inbox if it passes. If it fails, the email may be treated with suspicion or flagged as spam.

Implementing DKIM involves a few key steps:

  • Generate key pair: You need to generate a DKIM key pair consisting of a private key (kept secure on your email server) and a public key (published in your domain's DNS records).

  • Configure your email server: Your email server software needs to be configured to use the private key when signing outgoing emails.

  • Update DNS records: You'll need to add DKIM records to your domain's DNS settings, which include the public key and other DKIM-related information.

  • Test and monitor: After implementation, it's essential to thoroughly test your DKIM setup and monitor it for any issues.

By mastering DKIM, you're taking a significant step toward ensuring the integrity of your email communications and bolstering your email deliverability. 


What is SPF?

Sender Policy Framework, commonly known as SPF, is a fundamental email authentication protocol that helps protect your domain from email spoofing and phishing attacks. At its core, SPF is a straightforward method to validate the authenticity of the sender of an email. It specifies which mail servers are authorized to send emails on behalf of your domain. When an email is received, the recipient's mail server checks whether the sender's IP address matches the list of authorized servers in your SPF record.

Here's how SPF plays a pivotal role in email authentication:

  • SPF record: As a domain owner, you create an SPF record in your DNS settings. This record lists the IP addresses or domains of email servers permitted to send emails on your behalf.

  • Receiving server check: When an email is received, the recipient's mail server performs a DNS lookup to retrieve your SPF record. It then compares the sender's IP address with the authorized servers in your SPF record.

  • Authentication result: Based on the SPF check, the receiving server assigns an SPF "pass" or "fail" status to the email. If it passes, the email is considered authentic; if it fails, it may be treated as suspicious or marked as spam.

Implementing SPF involves the following steps:

  • Create your SPF record: Define the authorized IP addresses or domains in your SPF record. You can specify multiple servers or services that are allowed to send emails on your behalf.

  • Publish SPF record: Add the SPF record to your domain's DNS settings. This record should be publicly accessible for receiving mail servers to verify.

  • Test and monitor: After implementation, test your SPF record to ensure it's working as expected. Regularly monitor it for any changes or issues.

By simplifying SPF authentication, you're strengthening your email security, reducing the risk of email impersonation, and enhancing email deliverability. 


Best Practices for Email Deliverability

Achieving expert-level email deliverability is a multifaceted goal that involves more than just mastering authentication protocols like DMARC, DKIM, and SPF–it also involves adopting best practices related to content, list management, and reputation management. But, first and foremost, maintaining a strong authentication setup with DMARC, DKIM, and SPF, correctly configured and aligned with your sending domains, is crucial.

Create Engaging (and Compliant) Content

When it comes to content, personalization is key. Tailor your emails to individual recipients based on their preferences and past interactions with your brand. Avoid spammy tactics, such as trigger words and misleading subject lines, which can raise red flags for spam filters. Optimize images and maintain a balanced text-to-image ratio to improve accessibility and avoid spam filters.

Build and Manage a Clean Subscriber List

Building and maintaining a clean, engaged subscriber list is equally important. Implement a double opt-in process to ensure that subscribers genuinely want to receive your emails. Regularly clean your list by removing inactive or unengaged subscribers, as sending to uninterested recipients can harm your sender reputation. Segment your email list based on user behavior, demographics, or preferences to send targeted, relevant content. Always obtain explicit permission before adding someone to your email list, avoiding purchased or scraped lists, which can lead to high bounce rates and spam complaints.

Monitor and Maintain Sender Reputation

Monitoring and maintaining your sender reputation is an ongoing process. Keep a close eye on your sender reputation using available tools and services that provide insights into your sender score and reputation. Set up feedback loops with major email providers to receive notifications of spam complaints and address any issues promptly. Maintain a consistent sending schedule and volume to avoid triggering spam filters with sudden, drastic changes. Lastly, manage bounces, unsubscribes, and spam complaints promptly and automatically to demonstrate a commitment to maintaining a clean list. 

By incorporating these best practices into your email marketing strategy, you'll not only enhance email deliverability but also improve engagement, build trust with your audience, and contribute to the overall success of your campaigns.


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Nicole is a copywriter turned content manager, experienced in all things writing and editing. Based in Brooklyn, NY, she is always on the hunt for the best New York-style pizza, in addition to being an avid reader, traveler, and yogi.

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