The New Importance of ALT Text in Email Deliverability

When it comes to email marketing, we often focus on technical aspects like DKIM (DomainKeys Identified Mail), SPF (Sender Policy Framework) and DMARC (Domain-based Message Authentication, Reporting and Conformance) to ensure email deliverability. These authentication protocols are critical for verifying sender identity and preventing spam. However, marketers are now realizing that non-technical factors — like email image alternative text (ALT text), the descriptive text that appears when an image fails to load — play a growing role in deliverability and engagement.

In this post, we’ll explore how ALT text is evolving from an accessibility best practice into a key factor for email performance. We’ll also show how combining ALT text optimization with DKIM, SPF and DMARC can improve both deliverability and engagement.

The Shift Toward ALT Text’s Importance

Originally, the primary purpose of ALT text was to improve accessibility for visually impaired users and enhance SEO by providing textual content for images. But as inbox algorithms become more sophisticated, ALT text has emerged as a subtle but significant deliverability signal.

Here’s why:

Image-heavy emails without text can trigger spam filters. Filters prioritize well-structured emails with meaningful content over graphics-only emails, which spammers often use.
ALT text ensures message readability even if images are blocked by a recipient’s email client or settings. If your email makes sense without the images, it will be seen as higher-quality content.
Engagement metrics affect deliverability. Emails that are more readable — thanks to ALT text — are more likely to generate clicks, improving sender reputation over time.

As inbox providers like Gmail, Outlook and Yahoo! Mail increasingly rely on user behavior and content quality to decide what lands in the inbox versus the spam folder, emails with properly optimized ALT text are better positioned to succeed.

How ALT Text Complements DKIM, SPF and DMARC Authentication

While ALT text is more content-focused, DKIM, SPF and DMARC are technical protocols that help prove the authenticity of an email. Here’s a quick breakdown of how these protocols work:

DKIM: Adds a digital signature to emails, verifying that the message hasn’t been altered during transit.
SPF: Ensures that only approved IP addresses can send emails on behalf of your domain.
DMARC: Aligns DKIM and SPF results to prevent spoofing and phishing attacks.

Without these protocols in place, emails are more likely to land in spam folders, regardless of their content. However, authentication alone isn’t enough. Even properly authenticated emails can still get filtered if they appear spammy or generate poor engagement rates. This is where ALT text plays a vital role by supporting good design and readability, ensuring recipients interact with your emails.

Best Practices for Using ALT Text to Improve Deliverability

Content quality and user engagement have become equally important, and ALT text plays a surprisingly pivotal role in this new landscape. Well-optimized ALT text ensures your emails remain readable, accessible and engaging, even if images don’t load.

To maximize the benefits of ALT text in combination with authentication protocols, follow these best practices:

Describe the content, not just the function: Instead of saying “Image of a button,” write “Click here to learn more.” This makes the email actionable, even if images don’t load.
Keep ALT text concise: A short, relevant description works better than lengthy text that might overwhelm screen readers or get truncated.
Use ALT text strategically for calls to action (CTAs): If a CTA button is an image, the ALT text should still make the action clear (“Sign up now,” “Start your free trial”).
Check your email’s rendering with images blocked: Preview your email in Gmail and Outlook with images disabled to ensure it’s readable.
Balance images with plain text: Emails with a better image-to-text ratio (about 60% text to 40% images) are less likely to be flagged by spam filters.

By expanding your use of robust authentication protocols and thoughtful content design to include ALT text, your emails are more likely to cross the first hurdle of reaching inboxes and, ultimately, engaging recipients.