Does plain text email version affect deliverability?
Michael Ko
Co-founder & CEO, Suped
Published 1 May 2025
Updated 19 Aug 2025
9 min read
For years, the question of whether a plain text email version affects deliverability has been a topic of debate in the email marketing and security communities. While many senders focus primarily on the visual appeal and interactivity of HTML emails, the plain text counterpart often gets overlooked or auto-generated without much thought. Yet, its presence, or absence, can subtly influence how inbox providers perceive your messages.
The underlying principle is quite simple: email is designed to be accessible. Not all email clients can render HTML perfectly, and some users prefer text-only viewing for accessibility reasons or simply to reduce visual clutter. This is where the plain text version comes into play, serving as a fallback or alternative display for your email content.
However, the impact on deliverability isn't always straightforward. Some sources claim that plain text emails have inherently higher deliverability rates due to their simplicity and lower likelihood of triggering spam filters, while others argue that a properly coded HTML email with a corresponding plain text version is the ideal approach. We will explore both sides and provide clarity on this crucial aspect of email sending.
The role of plain text versions
Every time you send an HTML email, it should ideally be a multipart/MIME message, meaning it contains both an HTML part and a plain text part. This ensures that recipients using different email clients or settings can still view your message content. The plain text version is a simplified representation of your HTML email, stripping out all formatting, images, and complex layouts.
Many email service providers (ESPs) and marketing platforms automatically generate a plain text version from your HTML content. While convenient, this automatic generation can sometimes lead to issues. For instance, some automated processes might convert bolded text into ALL CAPS, which can be perceived negatively by spam filters, especially those used by Microsoft. This specific formatting issue can inadvertently harm your email deliverability, pushing messages into the spam folder instead of the inbox.
The primary role of the plain text version, from a deliverability standpoint, is to prevent your email from looking like hashbusting, a technique spammers use to bypass filters by sending only an HTML part with obfuscated content. Including a coherent plain text part signals to inbox providers that your email is legitimate. It acts as a safety net, ensuring your message can be read regardless of the recipient's email environment, and plays a small yet significant role in avoiding blocklists (or blacklists).
Deliverability impact
The general consensus among email deliverability experts is that including a plain text version is indeed important for email deliverability. While modern, large-scale inbox providers (like Gmail, Yahoo, Outlook) are sophisticated and unlikely to flag an email solely for lacking a plain text part, some older or more aggressive spam filters might. These filters might assign a higher spam score to emails without a plain text alternative, increasing the chance of landing in the junk folder.
The impact isn't always direct, but rather a cumulative effect of various factors contributing to your overall sender reputation. A missing plain text version, combined with other less-than-optimal practices (e.g., poor image-to-text ratio or suspicious links), can push an otherwise borderline email into the spam folder. Plain text emails often have higher deliverability because they present a much smaller attack surface for malicious content.
It is not so much that a plain text email version guarantees deliverability, but its absence or poor quality can definitely contribute to issues. Ensure that if you're sending HTML, you're also providing a clean, readable plain text alternative.
The deliverability impact
While HTML emails offer rich formatting and visual appeal, plain text versions are crucial for ensuring broad compatibility and improving deliverability. Many spam filters specifically check for the presence and coherence of the plain text part. A missing or nonsensical plain text version can raise red flags with providers and increase the likelihood of messages being filtered as spam or blocked outright.
It is important to remember that not all mailboxes are created equal, and some smaller, more aggressive spam filters or corporate firewalls may block emails lacking a plain text part more readily than larger providers like Google, Yahoo, or Microsoft.
Best practices for plain text
Even with automated plain text generation being common, it is a best practice to at least review, if not manually edit, your plain text version. This helps ensure it's readable and accurately reflects the HTML content, without introducing spam triggers like excessive capitalization or broken links. The plain text should convey the core message and calls to action clearly.
Review auto-generated versions: Check for formatting issues, especially unwanted ALL CAPS, which can be seen as spammy behavior. Ensure that any automated processes handle bolded text gracefully without causing red flags.
Maintain content parity: While it doesn't need to be identical, the plain text version should broadly match the HTML content. Major discrepancies can signal suspicious activity. For instance, if your HTML version discusses one topic but your plain text discusses another, it might raise concerns with spam filters.
Include clear links: Ensure all important links from your HTML email are present and clearly visible in the plain text version. Users who view the plain text version still need to be able to navigate to your content. Avoid using HTTP links if possible, as HTTPS is generally preferred for security and trust.
Consider accessibility: A well-crafted plain text version improves accessibility for users who rely on screen readers or prefer minimal interfaces. This wider reach can also indirectly contribute to better engagement, which positively impacts deliverability.
While the manual effort might seem significant, especially for high-volume senders, many platforms offer tools to automate and customize the plain text generation, striking a balance between convenience and deliverability best practices. It's often not about ditching HTML for plain text, but rather ensuring that both versions are optimized and coexist effectively within a multipart email.
HTML versus plain text
The choice between HTML and plain text isn't an either/or dilemma for most marketing emails today. The industry standard is to send a multipart/MIME email, which includes both versions. This ensures that the email displays correctly across all clients and user preferences. However, understanding the strengths of each format can help you optimize your campaigns.
HTML emails allow for rich design, branding, images, and interactive elements, which can significantly enhance user experience and boost engagement metrics. However, they can also be more susceptible to spam filtering if not coded cleanly or if they have a high image-to-text ratio. On the other hand, plain text emails are lean, load quickly, and are inherently less likely to trigger spam filters due to their lack of complex code. Plain text emails have wider reach due to their accessibility and compatibility.
HTML emails
Pros: Visually engaging, supports branding, rich media (images, videos), and interactive elements. Allows for detailed tracking and analytics of user behavior within the email.
Cons: Can be more prone to spam filtering if poorly coded, has an excessive image-to-text ratio, or contains suspicious elements. Loading speed can be affected by heavy content. Not all email clients render HTML perfectly, leading to inconsistent display.
Plain text emails
Pros: Higher deliverability due to simplicity, less likely to trigger spam filters. Faster loading and universal compatibility across all email clients and devices. Better for accessibility and users who prefer minimal interfaces. Often perceived as more personal and direct.
Cons: Lacks visual appeal and branding elements. No rich formatting (bold, italics) or clickable buttons, which can limit engagement. Less data for tracking user interaction compared to HTML emails. Manual creation can be time-consuming.
The key is to leverage the strengths of both. Always include a well-formatted plain text version alongside your HTML email. This dual approach maximizes your chances of reaching the inbox and ensures that all subscribers can access your message, regardless of their email client or preferences. Properly coded HTML emails with a clean plain text counterpart are the standard for deliverability.
Views from the trenches
Best practices
Always include a plain text version in multipart/MIME emails to support all clients.
Review auto-generated plain text for formatting issues like ALL CAPS or broken links.
Ensure the plain text content roughly matches the HTML version to avoid spam flags.
Prioritize readability in the plain text version, ensuring core message and calls to action are clear.
Automate the plain text generation process if manual efforts are not feasible.
Common pitfalls
Omitting the plain text version entirely, risking blocks by stricter spam filters.
Relying solely on poorly implemented auto-generated plain text that contains spam triggers.
Significant content discrepancies between the HTML and plain text versions.
Not checking how the plain text version renders in various email clients.
Assuming all major inbox providers will ignore a missing or bad plain text version.
Expert tips
Focus on the overall sender reputation, where the plain text version is one of many contributing factors.
For cold outreach, consider sending plain text emails to establish a solid sender reputation.
If building an ESP or sending platform, ensure the plain text converter is robust and handles various HTML structures.
Understand that aggressive spam filtering by smaller providers might apply stricter rules.
Prioritize the core message and links in the plain text version for universal access.
Expert view
Expert from Email Geeks says deliverability is generally unaffected by minor plain text versus HTML mismatches.
2022-11-04 - Email Geeks
Marketer view
Marketer from Email Geeks says auto-generated plain text versions are often unreadable, though rarely seen by recipients.
2022-11-04 - Email Geeks
Final thoughts on email formatting
While the plain text version of an email may not be the primary factor determining deliverability for major inbox providers, its role is still significant. It acts as a crucial fallback for recipients, ensures accessibility, and can influence how some spam filters (or blocklists) perceive your message. Neglecting the plain text version can lead to subtle yet impactful deliverability issues, especially when combined with other suboptimal sending practices.
The safest and most effective approach is to always include a well-formatted plain text version alongside your HTML email. Whether you choose to manually craft it or rely on a robust auto-generation tool, ensure it accurately reflects your message and avoids elements that might trigger spam flags. This diligence contributes to a stronger sender reputation and better overall inbox placement, helping you boost your email deliverability rates.
Ultimately, an email that is both visually appealing and universally accessible is an email that is more likely to reach its intended audience and achieve its marketing goals. Always prioritize the user experience, which includes ensuring your content can be consumed by everyone, regardless of their email client limitations. Remember that plain text emails are slightly less likely to be filtered into spam folders due to their inherent simplicity.
Microsoft. This specific formatting issue can inadvertently harm your email deliverability, pushing messages into the spam folder instead of the inbox.
Yahoo, Outlook) are sophisticated and unlikely to flag an email solely for lacking a plain text part, some older or more aggressive spam filters might. These filters might assign a higher spam score to emails without a plain text alternative, increasing the chance of landing in the junk folder.
Google, Yahoo, or Microsoft.
