Understanding Email Deliverability in Marketo

  • Nick Donaldson

    Nick Donaldson

    Director of Growth Marketing, Knak

Published Jun 27, 2024

Understanding Email Deliverability in Marketo


Improve email deliverability in Marketo with tips on sender reputation, content design, list management, and technical setup for better inbox placement.

It's the perfect Marketo email campaign: images are on point, copy barbed with hooks, personalized content, and a clear call-to-action. You hit send, feeling confident in your success. However, when you check the metrics, the number of opens is dismal, and clicks are non-existent. What went wrong?

You can do everything right, but if your emails suffer from poor deliverability, you’ll struggle to succeed. Understanding and optimizing your Marketo instance for email deliverability is crucial—if you’re not landing in the inbox, then how can your efforts in images, copy, and content pay off?

In this guide, we're going to look at the specific details of email deliverability within the Marketo platform.

The basics of email deliverability in Marketo

Let’s start with the basics of email deliverability in Marketo. Multiple components contribute to ensuring your emails are delivered, and all are within your control. Here's what we'll cover in this section:

  • Managing sender reputation
  • Email content and design
  • List management and hygiene

Managing sender reputation in Marketo

Sender reputation is a trust score assigned to your email sending domain and IP, used by ISPs (Internet Service Providers) and Email Service Providers (ESPs) to decide whether to accept, reject, or filter your emails. Your organization's sender reputation has a big role to play in deliverability and maintaining a good reputation is critical to your success.

There are several components of sender reputation in Marketo that you can monitor, including:

  • Bounce rates
    • A high bounce rate indicates poor list management practices. Bounces can be either hard bounces (permanently unresponsive or non-existent email addresses) or soft bounces (resulting from full inboxes or server issues).
  • Spam complaints
    • Google’s spam complaint threshold is an example of how being flagged by users for sending ‘spammy’ emails could result in deliverability penalties.
  • Sending practices
    • Suddenly sending a large number of emails can be viewed as suspicious, and organizations with larger email lists may engage in IP warming practices (more on that below).
  • Authentication
    • Ensure you have correctly configured security settings such as SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance).
  • Engagement rates
    • Monitoring recipient engagement with your emails through opens, clicks, and unsubscribe rates serves as an early warning system for your sender reputation.

We'll get into the details of each of these elements but for now it's important to know that sender reputation is a combination of factors that must be carefully managed.

Email Content and Design Best Practices in Marketo

Creating high-quality, engaging email content is a good way to ensure long-term deliverability. Marketo provides tools that help optimize your email content and design for high deliverability. For example, ensure your emails are mobile-friendly; use Marketo’s email editor to preview and optimize them for different devices. You can also use no-code email creation tools like Knak to take care of mobile and responsive design automatically.

You should also avoid relying too heavily on images in your emails. Image-only emails have many pitfalls and are regularly marked as spam by email service providers. While images can significantly enhance email engagement, it is crucial to maintain a balance in their usage.

List Management and Hygiene in Marketo

Clean email lists are fundamental to high deliverability. Marketo offers features to help you keep lists clean and ensure good email hygiene. A common challenge for email marketers is that over time, email lists become stale—subscribers move on from their roles, email addresses are deactivated, and subscribers sometimes become unengaged. This can lead to high bounce rates, negatively impacting both deliverability and sender reputation.

A key component of email list management is regular list cleaning. Using Marketo’s Smart List functionality, you can segment and filter contacts who have stopped opening emails, are returning hard bounces, or appear otherwise inactive. You can either remove them entirely from the database or sequester them from your main marketing lists. This will help keep engagement high and bounce rates low.

You should also adopt a proactive approach to list management by implementing double opt-in practices, ensuring that only interested subscribers are added. In the era of privacy regulations such as GDPR and CCPA, employing strong compliance mechanisms can help future-proof your email engagement and ensure adherence to legal requirements.

Lastly, providing clear unsubscribe options for users is important. While unfortunate, an unsubscribe isn’t necessarily negative; it allows users to self-select based on their interests and helps automatically regulate the cleanliness of your lists. You can help mitigate this by using a preference center that gives users more options for managing their communication preferences with you.

Technical Aspects of Email Deliverability in Marketo

Achieving high email deliverability requires not only great content and thoughtful list management but also a solid technical foundation. The technical aspects of email deliverability in Marketo are crucial for long-term success. Here's what we'll cover:

  • Authentication protocols (SPF, DKIM, and DMARC)
  • DNS configuration
  • IP Warming

Authentication protocols in Marketo

Authentication protocols have been an integral part of email marketing history. Each protocol—SPF, DKIM, and DMARC—plays a slightly different role in email authentication. Together, these protocols enhance the safety of email marketing for consumers and your users by validating that email senders are who they claim to be. Similarly, they protect your brand by preventing bad actors from impersonating you to deceive consumers.

Let's take a deeper look at each authentication protocol.

Sender Policy Framework (SPF)

The Sender Policy Framework (SPF) is an email authentication method designed to detect and block email spoofing. It allows domain owners to specify which IP addresses are authorized to send emails on behalf of their domain. IP addresses function like physical addresses in the real world—if an email comes from an unregistered IP address, the ESP will recognize and flag the email as suspicious.

DomainKeys Identified Mail (DKIM)

DomainKeys Identified Mail (DKIM) is an email authentication method that uses cryptographic signatures to ensure that email content remains unaltered during transit. Think of DKIM as a specialized signature that verifies the integrity of the email contents and the sender. SPF and DKIM are both essential for modern email authentication.

Domain-based Message Authentication, Reporting, and Conformance (DMARC)

Domain-based Message Authentication, Reporting, and Conformance (DMARC) builds on the SPF and DKIM protocols by adding a policy that directs ISPs on how to handle emails that fail authentication checks. DMARC enables proactive protection of your domain from phishing and spoofing attacks by offering a mechanism to review suspicious emails. Together, SPF, DKIM, and DMARC constitute the triumvirate of email authentication protocols.

Proper DNS Setup for Email Authentication in Marketo

As part of setting up authentication protocols such as SPF, DKIM, and DMARC, you must ensure your DNS is configured correctly. Your DNS (Domain Name System) functions as your listing in the world’s digital phonebooks. Your DNS records contain crucial information about your IP address and your email authentication details.

As part of your setup with Marketo, you will need to collaborate with your IT team to properly configure your DNS. This includes whitelisting Marketo IP addresses to ensure that your organization sends legitimate emails from those addresses. It also involves adding TXT records with information about your SPF, DKIM, and DMARC records.

IP warming in Marketo

IP warming is the process of gradually sending small batches of emails to acclimatize ISPs to your sending behavior. During the warming phase, you will gradually increase the volume of emails sent. IP warming helps establish your sender reputation with ISPs as a legitimate email sender.

To implement IP warming in Marketo, follow these steps:

  • Start with a small volume of emails to your most engaged subscribers and gradually increase this volume over the course of days and weekends.
  • Closely monitor engagement to ensure metrics such as open rates, click rates, bounce rates, and unsubscribe rates stay within acceptable limits.
  • Adjust your email sending strategy as needed, potentially pausing the IP warming process if necessary.
  • Maintain consistent email sending practices to build a positive sender reputation over time. Avoid sudden surges in email volume.

Email Deliverability Metrics in Marketo

Monitoring email deliverability in Marketo is crucial for protecting your sender reputation from negative impacts. With Marketo email reports, you can track deliverability metrics and take corrective action before issues arise.

Here's an overview of email deliverability metrics and how they could impact your marketing efforts.


Bounce Rate - Hard Bounces


Occur when an email is sent to an invalid, closed, or non-existent email address.


High hard bounce rates indicate poor list quality and can harm your sender reputation.


Bounce Rate - Soft Bounces


Temporary issues such as a full inbox or a server problem.


While less critical than hard bounces, consistently high soft bounce rates should be monitored and addressed.


Open Rates


The percentage of recipients who open your email.


High open rates indicate that your subject lines are effective and your emails are reaching engaged recipients.

Low open rates could signal issues with your sender reputation or subject lines. Consistently low open rates might lead ISPs to classify your emails as spam.


Click-Through Rates (CTR)


The percentage of recipients who click on one or more links within your email.


High CTRs indicate that your email content is engaging and relevant.

Low CTRs may suggest that your content isn’t resonating with your audience, potentially affecting future engagement and deliverability.


Spam Complaint Rates


The percentage of recipients who mark your email as spam.


High spam complaint rates are a significant red flag for ISPs. If too many recipients mark your emails as spam, your sender reputation will suffer, and ISPs may block your emails entirely.


Unsubscribe Rates


The percentage of recipients who opt-out of your email list after receiving an email.


While unsubscribes are not as harmful as spam complaints, a high unsubscribe rate indicates that your content might not be meeting recipients’ expectations. Consistently high unsubscribe rates can signal engagement issues and negatively impact your sender reputation.


Delivery Rates


The percentage of emails that were successfully delivered to recipients’ inboxes. This metric excludes bounced emails.


Low delivery rates can indicate issues with list quality or sender reputation.


Inbox Placement Rate


The percentage of emails that are delivered to the inbox versus the spam or junk folder.


A high inbox placement rate is crucial for engagement. Low rates may indicate problems with your sender reputation or email content.

Achieving high deliverability for a better user experience

Achieving high deliverability is clearly beneficial for your marketing efforts, yet it involves more than just having a solid technical foundation. While a solid technical foundation provides a strong base, delivering a quality user experience with each email is key to long-term success. Engaging subscribers with authentic, meaningful content is the best way to ensure sustainable deliverability in Marketo.

User experience begins with well-designed emails. Tools such as Knak enable the creation of professional, fully responsive emails without writing a single line of code. This enables marketers to craft beautiful emails without navigating the complexities of mobile design or mastering Marketo’s email syntax. Consistently great emails, every time.

If email deliverability in Marketo is top of mind, check out our video demo to see how you could start building emails today.

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  • Nick Donaldson


    Nick Donaldson

    Director of Growth Marketing, Knak

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