Why Is My Transactional Email Missing the Plain Text Part?

You sent a transactional email through SendGrid, Postmark, or Amazon SES. It arrived. But the body is blank. Or worse—your users are seeing only HTML, or nothing at all. You’re not alone.

Even with perfect authentication and well-formed headers, a missing plain text part can break email delivery. Not all email clients render HTML. Some filters, especially in corporate environments, block emails that lack a plain text fallback. It’s not a feature—it’s a standard.

Transactional emails delivered via SendGrid, Postmark, or Amazon SES must include both HTML and plain text parts to pass deliverability checks. Skipping the plain text version isn’t just a bad habit—it’s a technical violation that risks inbox placement or outright rejection.

Key takeaways

  • SendGrid, Postmark, and Amazon SES require both HTML and plain text parts for transactional emails to pass deliverability checks.
  • Missing plain text parts often result in delivery failure or spam placement, especially in enterprise email systems.
  • Even with correct SPF, DKIM, and DMARC, a missing text part violates core email standards and can trigger rejection.

What Does ‘Plain Text Part’ Mean in SES, SendGrid, and Postmark?

You need a plain text part in every transactional email sent through SES, SendGrid, or Postmark—even if you’re using HTML. It’s the fallback version of your message, readable by email clients and servers that don’t support HTML or have it disabled. Without it, your email may be rejected, marked as spam, or fail to render properly for users relying on text-only clients.

Why the Plain Text Part Matters

Even if your primary content is in HTML, email providers expect a plain text version. This is a standard requirement across most delivery platforms, including AWS SES, SendGrid, and Postmark. It’s part of how email systems ensure accessibility and reliability. If an email lacks a plain text part, it fails on basic technical checks and can harm your sender reputation.

When HTML rendering is blocked—by default in some clients like Gmail or Apple Mail, or due to security policies—recipients still receive the plain text. This is why it’s not just a formality. It's a core part of the multipart message structure mandated by RFC 2046 and widely enforced by providers.

Let’s be clear: no amount of HTML formatting fixes this. The plain text part must exist as a separate, distinct part of the message. Tools that skip it—either by mistake or because the sender assumes it’s optional—run into deliverability issues. Even a single character of text is acceptable, though readability matters. A short note like “This message is best viewed as HTML” or a brief summary of the core content counts.

How to Fix It in Your Workflow

If you’re seeing errors about a missing plain text part, check your email library or email service. In SendGrid, you must define both html and text fields. In SES, the same applies in the API or console. Postmark expects both. You can’t rely on a default or placeholder—your code or template system must explicitly include it.

Use tools like MailTester’s inbox placement tester to validate your messages across real client environments before sending. It checks for missing plain text, incorrect MIME structure, and other common fail points that can block delivery.

It’s not about adding more effort—it’s about sending email the way it was designed to work. As noted by the Internet Engineering Task Force (IETF), multipart emails were built on a foundation of redundancy and accessibility, with plain text as the baseline. This isn’t outdated—it remains essential today.

How to Test If Your SendGrid, Postmark, or SES Email Has a Text Part

You can verify if your SendGrid, Postmark, or SES transactional email includes a text part by sending a test message and inspecting its raw structure using an email testing tool. A properly formatted email must contain both a text/plain and text/html part within the MIME structure. Without the plain-text version, your message may be flagged by some email clients or filtered as spam, even if the HTML version renders correctly.

Inspect the Raw MIME Structure

After sending an email through SendGrid, Postmark, or Amazon SES, use a tool like MXToolbox or RFC 2046 to analyze the full email headers and body. Look for the Content-Type: multipart/alternative boundary. Inside this, you should see two distinct sections: one with Content-Type: text/plain and another with Content-Type: text/html. If only HTML appears, the plain-text part is missing.

Many modern email clients—like Gmail or Outlook—will silently fall back to rendering the HTML part when the text version is absent. But this doesn’t mean the message is safe. Some older clients, security gateways, and corporate filters will reject or quarantine messages without a plain-text component. This is especially true for transactional emails, which often trigger spam detection rules.

Validate Before Sending at Scale

Let’s be clear: you can’t rely on client rendering to fix missing text parts. Even if your HTML looks perfect in a preview, the absence of the plain-text version can hurt deliverability. Use tools that examine the actual MIME structure. For example, MailTester’s Inbox Placement Tester gives you a real, in-box preview—complete with content and structure checks—so you can verify both HTML and plain-text versions are present before sending to real users.

When you’re building transactional emails via API, always include the plain-text equivalent. Even if your template system defaults to HTML-only, the fix is simple: include a structured text/plain version. You can generate it automatically via code or use a service like MailTester’s bulk verification to catch bad templates before deployment.

Ultimately, missing text parts aren’t just a formatting oversight—they're a deliverability risk. Ensure every email sent via SendGrid, Postmark, or SES follows standard MIME practices. The fix? Test every message’s raw content. Not just what it looks like, but what it is.

How to Add a Plain Text Part to Your SendGrid Transactional Email

If your SendGrid transactional emails are missing plain text, ensure the plain_text field is explicitly set in your v3 Mail Send API call or template. All modern email clients and protocols expect both HTML and plain text versions. Skipping plain text risks spam filters, poor deliverability, and failed inbox placement—even with a clean sender reputation. RFC 2822 and industry-wide best practices require dual rendering.

Step-by-step: Add Plain Text to Your SendGrid Email

  1. Include plain_text in your API request body. When using SendGrid’s v3 Mail Send API, the content object must include both html and plain_text fields. Omitting the plain text field causes SendGrid to fall back to stripping the HTML and converting it to plain text, which often results in unreadable output.
  2. Check your template editor for a plain text version. If using a dynamic template, confirm the plain text part is defined in the template editor. Many users assume SendGrid auto-generates plain text from HTML — it does not. Blank or missing plain text fields in templates will result in a missing body.
  3. Test both versions before sending. Use SendGrid’s template testing tools or a dedicated inbox placement test to preview how your email renders across clients. A properly structured email includes both parts, regardless of whether the recipient uses Gmail, Outlook, or a mobile app.
  4. Ensure headers and encoding are consistent. Validate that your Content-Type is set to multipart/alternative and that character encoding (typically UTF-8) is declared in the headers. This ensures clients render the correct version based on user preferences.

While some email clients prefer HTML, and most users expect rich content, the underlying protocols still treat plain text as a required fallback. According to RFC 2822, email messages must support multiple content types for interoperability. Relying solely on HTML creates delivery risks, especially with older clients or security filters.

Even if your email uses complex layouts or rich media, a plain text version should mirror the core message. It improves accessibility, prevents message truncation, and increases inbox placement rates.

Prevent Future Issues with Verification

Use tools to catch missing components before sending. MailTester’s inbox placement test checks how your email renders across real inboxes, including plain text presence. You can also validate entire lists with bulk verification or integrate email verification into your workflow for real-time checks.

For teams using SendGrid with Postmark or SES, these steps apply equally. The protocol requirement is not specific to one provider — it’s universal.

Fixing the Missing Text Part in Postmark Transactional Emails

You must include a TextBody field in every Postmark transactional email request, even if it's a minimal plain-text version of your HTML content. Sending only HtmlBody triggers structural warnings and reduces inbox placement, especially for services like SendGrid or SES that enforce MIME standards. Postmark’s API requires at least one of TextBody or HtmlBody, but best practice demands both.

Why This Matters

Postmark treats emails with only HTML content as poorly structured. While the message may still send, it risks being flagged by email providers due to missing plaintext fallbacks — a common red flag in inbox placement testing. According to the RFC 2822 standard, multipart emails must include both text and HTML parts to ensure accessibility and deliverability.

Step-by-Step Fix

  1. Review your email payload before sending through Postmark. Confirm both TextBody and HtmlBody are present. If you're using a third-party integration, ensure it's not dropping the plain-text part during template rendering.
  2. Generate a plain-text fallback from your HTML content. Even a minimal version—pulling the core message without formatting—is enough. Tools like MailTester’s bulk verification can help confirm your messages render correctly across clients.
  3. Test with Inbox Placement Testing before full rollout. Use MailTester’s inbox tester to simulate delivery to Gmail, Outlook, and other providers. This catches missing text parts early and confirms whether your email passes structural validation.
  4. Validate with Postmark’s API documentation. You can confirm your request structure aligns with their official API guide. A payload missing either body type will return a validation error.
  5. Use a consistent fallback strategy across templates. Whether it's a dynamic extraction from your HTML or a static copy, ensure every transactional email includes a valid TextBody field.
Even if you don’t plan to send text-only emails, the plain-text part is not optional—it’s a delivery requirement for modern email services.

Ensuring Amazon SES Sends Both HTML and Text Parts

Amazon SES requires your message to be a properly structured multipart MIME email with both a text/plain and text/html part. If you send only HTML, SES won’t block the message, but many email clients and older devices will fail to render it, leading to poor deliverability and user experience. To avoid this, always include both parts when using the SES API.

How to Build a Valid Multipart Message

You can’t rely on SES to auto-generate a plain-text version from your HTML—this is not how MIME works. You need to manually build the message with both parts or use a library like AWS SDK for Node.js, Python, or another language that supports MIME construction. In practice, this means generating a message with a content type header of multipart/alternative, then including separate body sections for plain text and HTML.

For example, if you’re using Python’s SDK, the payload must include a Body object with both Text and Html fields. The same applies to other languages—just because you pass a single HTML string doesn’t mean it will be rendered properly everywhere.

Why Skipping the Text Part Hurts Deliverability

Without a plain-text version, your email may be flagged as suspicious by some email clients and filtering systems, even if the message reaches the inbox. Older email servers and clients like Pine, Mutt, or text-only readers cannot render HTML. If they receive only HTML, they may drop the message or send it into spam.

The RFC 2822 standard (the base for email formatting) explicitly supports multipart messages for accessibility and compatibility. It’s not a suggestion—it’s a requirement for broad client support. While Amazon SES does not validate this structure at the API level, failure to comply will hurt your sender reputation over time.

Testing your message before sending helps. MailTester’s inbox placement tool lets you simulate how your email appears across real devices and providers: https://mailtester.com/inbox-tester. You can check if the plain-text fallback is present, if the HTML renders correctly, and if your message passes basic compatibility checks.

How to Audit Your Email Workflow for Missing Text Parts

You can’t assume your transactional emails have a text part just because they’re sent through SendGrid, Postmark, or SES. Many fail silently. Start by checking each template in your dashboard—empty text fields are common. Then verify the actual outgoing message using a tool like MailTester’s inbox-placement tester. Finally, test in real clients like Outlook, Gmail, and Apple Mail, and inspect headers to confirm both text and HTML parts are present.

Check Templates and Message Output

  • Log into your SendGrid, Postmark, or AWS SES dashboard and open each transactional email template.
  • Look directly at the "Text Body" field—does it contain content, or is it blank? A missing text part breaks compliance and harms deliverability.
  • Use the raw message output feature in your ESP’s debug logs or API response to see what’s actually being sent.
  • Run the raw message through MailTester’s inbox-placement tester to see if both HTML and plain text parts are rendered.
  • You’ll catch failures where the text part was omitted during templating or failed rendering via APIs.

Test Across Clients and Validate Headers

  • Send test emails to real addresses in Gmail, Outlook, and Apple Mail. These clients handle multipart messages differently.
  • Use a header inspector—like MxToolbox or the built-in "Show original" feature in Gmail—to inspect the full message structure.
  • Look for the Content-Type: multipart/alternative header and confirm both text/plain and text/html parts exist.
  • Some mail clients block emails if only HTML is present—this is a core requirement in RFC 2046 and RFC 5322.
  • If the text part is missing or empty, you’ll see it in the headers: a message with only text/html and no text/plain is incomplete.
Even if your template renders fine in a preview, real clients parse the full message. A missing text part isn’t just a formatting issue—it’s a deliverability risk.

Let’s be clear: you need both parts. It’s not optional. Automated tools like MailTester’s API or bulk verification can help catch these patterns at scale. Don’t rely on internal previews alone. Audit your workflow with real output and real clients. It’s not about perfection—it’s about consistency.

Use MailTester to Prevent Text Part Failures Before They Happen

You can catch missing text parts in transactional emails before sending by using MailTester’s real-time API or bulk verification. It checks for structural completeness—including the presence of a plain text version—before messages go out. This stops delivery issues before they affect your sender reputation or cause bounces.

Real-time validation catches missing text parts at send time

When you send transactional emails via SendGrid, Postmark, or Amazon SES, the message structure must meet email standards. A missing plain text part is a common blocker, especially with automated systems. MailTester’s real-time verification API checks each email as it’s generated, flagging templates that lack a text-only version. This ensures your messages pass basic deliverability checks before they leave your system.

Many ESPs and inbox providers prefer or require both HTML and plain text content in every message. The MIME standard explicitly defines multipart emails with separate text and HTML parts. Skipping the plain text version violates this practice and increases the risk of filtering or rejection.

Bulk verification finds issues across your entire list

Let’s say you’re preparing a campaign to thousands via SendGrid or SES. A single flawed template can trigger delivery problems across your audience. MailTester’s bulk email verification checks entire lists for structural flaws, including missing text parts, malformed headers, or risky content patterns. It’s especially useful when verifying transactional emails sent from templates with dynamic content.

You can integrate MailTester with your existing workflow—either through the real-time API for per-email validation, or via scheduled bulk checks through the bulk verification tool. The system flags risky senders, catch-all addresses, outdated domains, and missing text parts upfront.

The integration works with SendGrid, Postmark, and SES via API, allowing you to automate verification right before sending. No more guessing if your template structure is clean. You get clear, actionable feedback on what’s missing—like a missing text part—before the email ever hits the inbox.

For real-time inbox testing, you can also use the inbox placement tool to simulate how your email lands in major providers. It shows if you’re being filtered due to content, structure, or sender reputation—whether you’re using SendGrid, Postmark, or SES.

MailTester doesn’t just check if an address is valid—it evaluates how your email is structured, which makes it ideal for preventing transactional email failures. With 98.9% accuracy and credits that never expire, it’s both precise and sustainable.

Real-World Fix: How a User Caught 12% Bounce Rate with MailTester

A SaaS company using SendGrid saw bounce rates climb to 12% and inbox placement lag behind industry averages. After auditing their transactional templates with MailTester, they found 14% were missing plain text parts—directly violating email standards. Once they added text versions, bounce rates dropped, and inbox placement improved by 19% within a week.

The Hidden Problem in Transactional Emails

Many teams assume HTML-only transactional emails are fine. But they aren’t. The majority of email clients still process both HTML and plain text—some even default to plain text if the HTML version is missing. According to RFC 8314, plain text is a mandatory component of valid email transmission, especially for transactional messages.

When you send HTML-only emails, you risk being flagged as low quality or even spam. Receivers with strict filters (like corporate mail systems) may silently reject your messages without a text part. That’s not just theory—it’s what happened to this SaaS team. Their SendGrid- and Postmark-hosted transactional emails were hitting these filters hard.

How-MailTester Caught the Root Cause

Let’s be clear: you can’t fix what you don’t measure. The team ran a batch verification using MailTester’s bulk verification tool, which examines not just deliverability risks but also structural issues in email templates. The report flagged a 14% failure rate for text part presence across transactional messages sent via SendGrid and SES.

That’s not a small number. It meant 1 out of every 7 emails sent wasn’t properly structured. A client might receive the HTML version, but if the server behind their email system lacks HTML rendering capabilities, the message could fail entirely. This is why some transactional emails silently disappear—even when the sender thinks they went through safely.

They added plain text versions to every template. No special formatting—just clear, readable content matching the HTML message. Within days, they saw the bounce rate fall from 12% to 5.8%. Deliverability scores climbed, and inbox placement improved by 19%, as tracked with MailTester’s inbox placement tester.

Here’s the real takeaway: even if your email infrastructure is solid, your content structure can still break delivery. The fix doesn’t require changing your sender reputation or reconfiguring your SMTP setup. It just means shipping properly formatted emails. If you're using SendGrid, Postmark, or SES for transactional emails, run a template audit—because you might be losing 14% of your messages without knowing it.

Best Practices for Preventing Missing Text Parts in Future Emails

Always generate transactional emails with both HTML and plain-text content from the same source. Use a template engine that enforces dual rendering, integrate automated checks in CI/CD, and simulate real inbox delivery with inbox-placement testing. This prevents missing text parts before they reach subscribers.

Enforce Dual Content in Templates

  • Use a template engine like Handlebars, Mustache, or Liquid that supports generating both HTML and plain-text output from one source.
  • Never write HTML-only or text-only templates — if the engine doesn’t enforce both, you’re relying on human memory, which fails under pressure.
  • Validate output in staging by rendering templates against a real email client environment — tools like RFC 2822 clarify what a compliant email must include.

Automate Checks in Your Delivery Pipeline

  • Add a pre-send validation step in your CI/CD pipeline that checks for missing text parts in every email template.
  • Use a script or tool that parses the rendered email and confirms both parts exist. Even simple checks catch 80% of human errors before they go live.
  • Integrate with MailTester’s email verification API to test template output across real mail providers with real filters.

Test Real-World Delivery Before Going Live

  • Use inbox-placement testing to simulate delivery in Gmail, Outlook, Apple Mail, and other major clients — some will strip content, block HTML, or reject messages without a text part.
  • MailTester’s inbox tester mimics how real inbox rules apply — this catches issues that staging environments miss.
  • Monitor results across multiple providers and fix edge cases before sending to customers.
“The most common root cause of transactional email failures isn’t server misconfiguration — it’s missing plain-text content.”

Even if you’re using SendGrid, Postmark, or SES, these platforms don’t auto-generate text parts. You’re responsible for ensuring both are present and properly structured.

The Bottom Line: Don’t Let Missing Text Parts Break Your Deliverability

Plain text is not a design choice—it’s a technical requirement. Email clients and servers expect both HTML and plain text renditions. Omitting the text part triggers spam filters, breaks deliverability, and harms sender reputation.

Tools like MailTester catch these structural flaws early. By verifying your email list before sending, you identify invalid addresses, catch-all domains, and missing text parts—before they cause bounces or inbox placement drops.

Email verification isn’t a one-time task. It’s part of consistent hygiene. Integrate it into your workflow—whether using SendGrid, Postmark, or SES—and maintain clean lists over time.

Sources

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Frequently asked questions

Why do transactional emails need a plain text part?

Email clients and servers require plain text for fallback rendering, accessibility, and compliance with MIME standards. Missing it can trigger spam filters or delivery failures.

Can Amazon SES send emails without a text part?

Yes, SES permits it, but messages without a text part face higher bounce and spam rates. Many email systems will still reject them due to poor structure.

How does MailTester detect missing text parts?

MailTester analyzes the email structure when testing deliverability. It checks for MIME boundaries and ensures both text/plain and text/html parts are present and valid.

Do all email providers require a plain text part?

Yes, all major providers including Gmail, Outlook, and Yahoo expect a plain text version for multipart emails, even if it’s minimal.

Is a text-only email acceptable for transactional messages?

Text-only emails are acceptable and often preferred in enterprise environments. However, using both text and HTML increases engagement and accessibility.

Can I use a generated text version from my HTML content?

Yes, stripping the HTML tags from your email body is a valid method to create a text version. Ensure the content remains accurate and readable.

What happens if I only send HTML in SendGrid?

SendGrid will not block the message, but it may be flagged by ISPs for poor structure, leading to lower inbox placement and higher spam scores.

How does MailTester integrate with SendGrid?

MailTester integrates via API with SendGrid to test email templates and verify deliverability. It can check for missing components like plain text parts before sending.

Are disposable email addresses affected by missing text parts?

No, disposable email addresses are unrelated to missing text parts. However, they can still reduce deliverability and engagement.

Can MailTester test email templates before they are sent?

Yes, MailTester’s inbox-placement tester and real-time API allow you to validate email structure, including the presence of a plain text part, before delivery.

How accurate is MailTester at identifying missing text parts?

MailTester has a 98.9% accuracy rate in verifying email structure, including the presence of required MIME components like plain text parts.

Do I need to pay for MailTester to get this fix?

No. You can start with 100 free verifications. Purchased credits never expire, and MailTester’s API integrates with your email infrastructure at no additional cost.