Planning, creating, and testing an email is a big investment of time and energy. But making sure it reaches your subscribers’ inboxes is critical. A good email deliverability rate isn’t just about solving issues after they happen—it’s about preventing them before you hit ‘send.’ 

Proactive strategies, like pre-send spam testing, help you catch and resolve potential issues early, ensuring your emails reach the inbox and maximize engagement.

Every email is a chance to connect with your audience and make a positive impact—but only if it lands in their inbox. This guide covers the essentials of email deliverability and how proactive measures can help make every send count.

What is email deliverability?

Email deliverability is the measure of whether your email reaches your subscribers’ inbox—whether that’s primary, social, or promotional—and avoids landing in the spam folder. 

It’s key to understand the difference between delivery and deliverability. While they sound similar, these terms refer to different stages of the email journey:

• Email delivery confirms that an email was accepted by the subscriber’s mail server without bouncing.
• Email deliverability evaluates how many of those delivered emails bypass spam filters and reach their intended destination in the inbox where subscribers are likely to engage.

Supporting both stages of deliverability, Litmus pre-send testing tools proactively identify potential issues—like sender reputation concerns or spam-triggering content—before they impact email campaign performance. Post-send monitoring then provides insights into where your emails actually landed, helping you refine and improve future sends.

Pre-send vs. post-send: catch issues early or respond quickly

A strong email strategy combines both pre-send and post-send tools, giving you a complete view of deliverability. 

• Pre-send testing: Pre-send tools allow you to address deliverability risks—like blocklist status or authentication issues—before you send. Resolving these in advance strengthens your chances of reaching the inbox.
• Post-send monitoring: Post-send tools analyze inbox placement across different email providers to reveal if your emails reached the inbox or spam. Going beyond typical ESP (email service providers) data, these insights enable you to troubleshoot effectively and optimize future campaigns.

Using both pre-send and post-send tools provides a well-rounded approach to email deliverability, making sure each send is set up for success.

Why Email Deliverability Matters

Email deliverability is worth every bit of attention you give it. Here’s why prioritizing deliverability helps your marketing go the extra mile:

Reach your audience

For subscribers to engage with your content, they first need to see it. High deliverability means your messages reach the inbox—right where your subscribers expect them.

Build trust and strengthen your reputation

Each email sent is an opportunity to build trust. Showing up in the inbox consistently (not the spam folder) reinforces credibility and loyalty with your audience. 

Adding Brand Indicators for Message Identification (BIMI) like your brand’s logo in the inbox, is one way to increase recognition and trust. In fact, BIMI can boost open rates by up to 21%, making your emails instantly recognizable and reassuring.

Maximize ROI from every campaign

With email marketing yielding up to $36 for every $1 spent, ensuring emails reach the inbox is essential. High deliverability means more visibility and engagement, boosting your ROI. 

Proactive pre-send testing tools like Litmus Spam Testing help secure deliverability by identifying issues before they reach the inbox, protecting brand email reputation and trust while keeping your emails on track to make the most impact.

Drive engagement and conversions

Improved deliverability means more eyes on your content. Each successful inbox placement strengthens your relationships with subscribers and inbox providers alike. Positive engagement signals, like opens and clicks, build credibility, improving your chances of inbox placement for future sends. Better deliverability means your emails reach more subscribers, driving traffic, engagement, and conversions with every send.

Maintain customer relationships

Consistently showing up in your subscribers’ inboxes builds brand love to increase the longevity of the customer relationship.  

What are key metrics for email delivery?

Monitoring key metrics is essential for achieving a high deliverability rate, ensuring you make the most of your budget and effort. 

Here are the metrics to keep a close eye on:

• Delivery rate: the percentage of emails the internet service provider’s (ISP) servers did not return or bounce.
• Bounce rate: the percentage of emails with temporary or permanent unsuccessful delivery, also known as bounced emails.
• Spam complaint rate: the percentage of your audience who mark an email as spam.
• Open rate: the percentage of your delivered emails that subscribers opened.
• Click-through rate (CTR): the percentage of how many people click on a call-to-action in your email.
• Unsubscribe rate: measures how many people opt out of your emails.
• Inbox placement rate (IPR): the percentage of your emails that make it to the inbox and not the spam folder.
• Sender reputation: a mix of factors that inbox service providers (ISPs) use to gauge whether you’re a trustworthy sender.

IP reputation—the perceived trustworthiness of the IP addresses you use for sending emails—also plays a key role in sender reputation. Building a positive IP reputation, particularly when using a new IP, requires a gradual increase in email volume, or IP warming. Following IP warming best practices helps establish trust with inbox providers, especially when transitioning to new providers or scaling up volume.

While delivery and open rates offer essential insights, post-send monitoring tools provide deeper visibility into inbox and spam folder placement. These tools go beyond basic ESP reports, giving you actionable insights to refine and improve future sends.

Master the email deliverability lingo

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Learn the terms

What factors affect email deliverability?

Strong email deliverability takes a proactive, strategic approach. Here are the core factors to focus on for better inbox placement and engagement:

The number of emails you send

Mailbox providers consider email volume and send frequency to assess whether an email sender might be engaging in spammy practices.

Email volume and send frequency

Email volume and frequency play a significant role in deliverability. A sudden spike in the volume of emails, especially from a new IP address, can trigger spam filters. Establishing a positive sender reputation from a new IP or domain requires a gradual volume increase—a process known as IP warming. 

IP warming is especially valuable during transitions to new providers, rebrands, or high sending volume marketing campaigns like Black Friday, helping build trust with inbox providers and ensuring consistent inbox placement.

Email content and formatting

Content quality matters. Spam filters review everything from subject lines to formatting to assess if an email could be spam. Litmus Spam Testing helps you stay ahead by flagging potential deliverability issues like blocklist status or unverified authentication, so each email is optimized for inbox placement.

List quality and engagement

Maintaining a clean, engaged list is essential for building a good reputation with Inbox Service Providers (ISPs). Regularly clean your list to remove inactive or invalid addresses and avoid spam traps—hidden addresses that catch senders with poor list hygiene. 

Re-engagement campaigns revive inactive subscribers, while personalization and segmentation keep content relevant, boosting engagement and signaling value to providers.

Sender reputation and authentication

Your sender reputation greatly impacts deliverability. Proper authentication protocols verify that your emails are legitimate, reducing the chance of being flagged as spam.

These include:

• Sender Policy Framework (SPF): Specifies which IP addresses can send emails for your domain, helping prevent spoofing.
• DomainKeys Identified Mail (DKIM): Adds a digital signature to your email to verify its authenticity and protect it from tampering.
• Domain-Based Message Authentication, Reporting, and Conformance (DMARC): Combines SPF and DKIM to guide inbox providers on handling unauthenticated messages, shielding your domain from phishing and spoofing.

Pre-send testing with Email Guardian

Confirming that authentication protocols are properly configured before sending is essential. Litmus’ Email Guardian offers 24/7 automated monitoring to verify your SPF, DKIM, and DMARC records, alerting you to authentication issues that could disrupt inbox placement. 

Proactive monitoring through Email Guardian’s automation maintains your sender reputation, helping meet evolving sender requirements from major providers like Google (Gmail) and Yahoo, and keeping your emails out of the spam folder.

Avoiding spam traps and blocklists

Spam traps and blocklists help inbox providers catch unwanted emails. Spam traps identify senders with poor list management, while blocklists flag domains and IPs associated with spam. 

Regular list hygiene and pre-send tools, like Litmus Spam Testing, help you sidestep these traps by identifying inactive contacts and confirming your domain’s blocklist status before sending.

Ensure your emails reach the inbox

Understand the factors affecting email deliverability. Implement best practices to make sure your emails reach your subscribers.

Boost deliverability

8 ways to improve deliverability 

Understanding what impacts email deliverability empowers you to take proactive steps to improve and maintain it. Here are some key actions to consider:

1. Make emails personal 

Subscribers opt-in to receive your messages because they value your brand. 

Personalization makes subscribers feel recognized, boosting engagement, conversions, and loyalty. Engage subscribers with tactics like:

• Combine segmentation and personalization to align with where subscribers are in their journey, tailoring future messages based on their interests.
• Use dynamic content to populate messages with product recommendations, exclusive offers, or relevant weather-based updates.
• Engage subscribers with interactive elements, like polls or surveys, to make your emails more engaging and valuable.

2. Maintain a clean and engaged email mailing list

Regular email list hygiene ensures you’re only reaching interested, valid contacts, which reduces the chances of hitting spam traps. Here are some ways to keep your list healthy:

• Use reputable list-building methods, avoiding purchased or rented lists to focus on genuinely interested contacts.
• Include a clear unsubscribe link in every email to help keep your list engaged.
• Run re-engagement campaigns for inactive subscribers, and remove contacts who remain unresponsive to improve deliverability.

3. Check your sender reputation

Your sender reputation directly influences inbox placement. Regularly monitor key metrics like domain and IP reputation, and use pre-send testing tools to proactively spot potential issues like blocklists or spam complaints before they impact deliverability.

4. Implement proper authentication

Email authentication shows inbox providers that your emails are legitimate, improving deliverability by reducing the chance they’ll be flagged as spam. Protocols like SPF, DKIM, and DMARC confirm your email’s authenticity, while BIMI builds brand trust and visibility by displaying your logo in supported inboxes. Authentication also protects your audience from phishing and spoofing risks.

5. Craft relevant and engaging email content

With subscribers spending only an average of 9 seconds reading an email, every element should count. Use these best practices to enhance quality:

• Keep your email list clean by removing invalid addresses.
• Optimize your email envelope (subject line and preview text) to improve open rates.
• Personalizing emails, using clear CTAs, and prioritizing value-driven, relevant content over overly promotional language. 

6. Use double opt-in

Double opt-ins verify subscribers’ intent to receive your emails, strengthening list quality and accuracy. This extra step reduces spam complaints and keeps bots off your list. 

At Litmus, we use a mix of single and double opt-ins—double for higher-volume pages to filter out bot accounts, and single for lower-risk content pages.

7. Monitor feedback loops

Email feedback loops provide insights into how your campaigns perform post-send, helping you fine-tune your strategy. Regularly review these metrics with your team to quickly adapt to trends and address emerging deliverability challenges.

8. Avoid spam traps

Keep your list current and avoid spam traps by removing inactive contacts and using email deliverability tools like Litmus Spam Testing. This allows you to identify and remove problematic addresses before sending, reducing risks to your deliverability.

How to test and optimize for email deliverability

Strong email deliverability depends on proactive testing and continuous optimization. Using both pre-send and post-send tools catches issues early and tracks performance, helping each campaign make a lasting impact.

Pre-send testing

Pre-send tools, like Litmus Spam Testing, flag potential deliverability obstacles before you hit send. These tools spot blockers such as blocklists, authentication errors, and content likely to trigger spam filters, optimizing your emails for inbox placement from the outset. Catching issues early reduces deliverability risks and increases the chances your emails land in subscribers’ inboxes.

Post-send monitoring

After sending, post-send tools track where emails land—whether they’re delivered to the inbox or spam folder. These insights reveal engagement rates like opens and clicks, showing trends and pinpointing areas for improvement. Post-send tools also offer deeper insights into placement across different providers, providing a complete view of your emails’ journey and supporting ongoing deliverability success.

A/B testing for engagement

A/B testing drives engagement—one of the most effective ways to improve deliverability. Testing elements like subject lines, CTAs, and layout shows what resonates most with your audience, boosting open and click-through rates. 

Higher engagement signals inbox providers that recipients value your emails, reducing the risk of them being flagged as spam. Regular A/B testing refines content to maximize these engagement metrics, strengthening sender reputation and improving inbox placement.

Deliverability is not a one-time task—it’s an ongoing process. ISP rules and audience behaviors evolve, making regular testing and optimization essential. With consistent fine-tuning, you can adapt to these changes and keep your emails reaching the right audience, consistently making an impact.

Ensure your emails make it to your subscribers inbox today!

Deliverability is vital to a healthy email marketing program. When emails don’t reach the inbox, your efforts and marketing dollars are less effective. 

Litmus Spam Testing scans your emails against 20+ spam filters, identifies issues, and offers actionable solutions. With automated deliverability testing, your emails reach subscribers without interrupting your workflow or requiring hours of manual testing.

Ready to improve your deliverability? Get started with Litmus Spam Testing today to keep your emails in the inbox where they belong.

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Originally published on April 5, 2022. Last updated November 22, 2024.