Does plain text email version affect deliverability?
Michael Ko
Co-founder & CEO, Suped
Published 1 May 2025
Updated 23 May 2026
7 min read
Summarize with
A plain text email version can affect deliverability, but it is rarely the deciding factor by itself. The stronger answer is this: send a proper multipart/alternative message with both HTML and plain text, keep the text version readable, and do not let automated conversion create junk.
I would not hand-edit every plain text version for deliverability alone. For most teams, the best workflow is auto-generation with guardrails: strip tracking clutter, preserve links in a clean way, avoid repeated all caps, include the unsubscribe line, and run test sends before campaigns. When a message is high-value, legal-heavy, or unusual in layout, then I would review the plain text manually.
The simplest practical test is to send the finished message through an email tester and inspect the MIME parts, authentication, links, and body rendering. Plain text is one input. Inbox placement still depends much more on sender reputation, authentication, engagement, complaint rate, list quality, and content patterns.
The direct answer
If the choice is "autogenerated plain text" versus "edited plain text", the deliverability winner is the version that is valid, readable, and broadly consistent with the HTML. Whether a person or a converter created it matters less than what ends up in the message.
- Use both parts. Send text/plain and text/html inside multipart/alternative for broad compatibility.
- Auto-generate first. Automation is fine when the output is clean and checked in pre-send QA.
- Edit selectively. Manual editing helps when templates have image-heavy layouts, many buttons, or dynamic content.
- Match the promise. The plain text does not need to be identical, but it should describe the same offer, sender, and required disclosures.
The real risk
The main risk is not that a plain text version exists. The risk is that the text part is empty, malformed, stuffed with tracking URLs, copied from old content, or so different from the HTML that it looks like content hiding.
- Empty text. An empty plain text part removes the compatibility benefit and looks careless.
- Old copy. A stale manual edit creates a stronger mismatch than a basic automated version.
- No QA. The plain text part should be visible in message previews and test reports before sending.
Autogenerated versus edited plain text
The safest operational answer is not "always manual" or "always generated". It is a workflow choice. Manual text gives more control, but it also creates more ways for a person to remove important copy or forget an update. Generated text gives consistency, but the converter needs sane rules.
Autogenerated text
- Best use. Recurring newsletters, lifecycle mail, product updates, and transactional templates.
- Main benefit. The text part stays tied to the HTML and is less likely to be forgotten.
- Main weakness. Converters can turn headings, buttons, and bold tags into awkward text.
Edited text
- Best use. Major launches, compliance-heavy mail, and templates with complex visual layouts.
- Main benefit. A person can make the text version concise, readable, and accessible.
- Main weakness. Manual edits drift over time unless they sit inside a strict approval process.
For most senders, I prefer generated plain text plus a review step for templates. If a marketer can freely delete the text part, paste unrelated copy, or remove the unsubscribe content, that is not a plain text strategy. That is a governance problem.
This also connects to whether you should still send multipart alternative emails. In practice, it remains a low-cost compatibility layer and a useful QA signal.
What filters care about
Flowchart showing how an email message is parsed and checked before inbox placement.
Modern mailbox providers do not treat plain text as a magic inbox pass. Large consumer mailboxes receive plenty of legitimate HTML-only mail every day. At the same time, some smaller or stricter filters score HTML-only mail a little more harshly, especially when the rest of the message already looks risky.
The plain text part matters most when it points to a broader content quality problem. A message with broken MIME, malformed HTML, excessive capitalization, suspicious links, or a hidden mismatch gives filters more reasons to distrust the email. A plain text part that simply mirrors the HTML in a readable way reduces that risk.
|
|
|
|---|---|---|
MIME shape | Medium | Bad structure can cause parsing issues. |
Text mismatch | Medium | Different offers can look deceptive. |
All caps | Medium | Generated emphasis can look spammy. |
Authentication | High | SPF, DKIM, and DMARC dominate trust. |
Complaints | High | Body format cannot offset bad consent. |
Plain text is a supporting signal, not the core reputation signal.
One common converter issue is worth calling out. Some HTML-to-text tools convert strong or bold content into ALL CAPS. A subject or body filled with uppercase words can look promotional or noisy, especially at providers that already see borderline engagement. Fix the converter rather than blaming plain text itself.
Email tester
Send a real email to this address. Suped opens the report when the test is ready.
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Preparing test address...
If an inbox test changes after removing all caps, shortening URLs, or cleaning broken MIME, treat that as a content and structure fix. The text part helped you find the problem, but it was not the only deliverability lever.
A safe plain text workflow
The best plain text process is boring. Build it automatically, expose it in QA, and restrict manual edits to people who know what must remain in the message. I want the text version to be useful to a human, not optimized into some fake deliverability trick.
- Generate from final HTML. Create the text part after personalization, conditional blocks, and legal footer logic are applied.
- Normalize formatting. Convert headings into plain sentences, keep line breaks readable, and remove repeated whitespace.
- Preserve intent. Keep the same offer, call to action, sender identity, unsubscribe method, and legal copy.
- Limit editing. Allow manual improvements, but block sends when the text part is empty or unrelated.
- Test the final MIME. Do not test a template preview only. Test the message exactly as subscribers receive it.
Healthy multipart structuretext
Content-Type: multipart/alternative; boundary="msg" --msg Content-Type: text/plain; charset=UTF-8 Thanks for reading. View the update: https://example.com/update Unsubscribe: https://example.com/unsubscribe --msg Content-Type: text/html; charset=UTF-8 <html> <body> <p>Thanks for reading.</p> <a href="https://example.com/update">View the update</a> </body> </html> --msg--
The text version above is not beautiful, but it is clear. It has the same core action as the HTML and includes the unsubscribe path. That is enough for most commercial mail.
When plain text starts to hurt
Plain text risk levels
Use these thresholds as QA triggers before a campaign leaves your sending platform.
Low risk
Send
Text is readable and matches the HTML offer.
Review
Edit
Text is generated but has awkward spacing or long URLs.
Fix
Hold
Text has all caps, missing footer copy, or broken links.
Stop
Block
Text is empty, unrelated, or structurally malformed.
Plain text starts to hurt when it sends a different signal than the HTML. A reader who opens the text part should understand the same message. Filters do not need exact word-for-word duplication, but a mismatch between the HTML body and the text body raises questions.
Malformed HTML can create the same kind of downstream problem because converters rely on the HTML tree. If the source HTML is broken, the plain text output can lose link labels, repeat hidden text, or flatten the layout into nonsense. That is one reason malformed HTML deserves its own QA check.
Block the send when this happens
- No text. The message has an empty text/plain part or no readable body.
- Wrong offer. The plain text promotes different terms, dates, pricing, or calls to action.
- Broken links. The text links are truncated, duplicated, or missing the unsubscribe path.
- Noisy caps. The converter turned emphasis into repeated uppercase copy throughout the body.
Where Suped fits
Plain text QA is useful, but it sits beside the larger email trust stack. Suped is our DMARC and email authentication platform, so the practical workflow is to use content testing for the message body and Suped for the domain-level signals that mailbox providers weigh every day.
Email tester sample report showing total score, email preview, issue summary, and per-section results
In Suped, I would use the email test report to inspect the rendered message, MIME structure, authentication result, and issues found in the body. Then I would use DMARC monitoring to watch real mail streams and catch authentication failures by source.
For a broader check, the domain health checker helps validate DMARC, SPF, and DKIM records. Suped also brings hosted DMARC, hosted SPF, SPF flattening, hosted MTA-STS, real-time alerts, and blocklist (blacklist) monitoring into one place, which matters more than tweaking a plain text version after every campaign.
Views from the trenches
Best practices
Generate plain text automatically, then review high-value templates before major sends.
Keep the text version readable, with the same offer, sender, footer, and unsubscribe path.
Test the final MIME output, because previews often hide converter and footer problems.
Common pitfalls
Letting editors delete the text body creates more risk than basic automated text.
HTML-to-text converters can turn bold copy into all caps that looks spammy in tests.
Treating plain text as a reputation fix distracts from DMARC, SPF, DKIM, and consent.
Expert tips
Use generated text for scale, but add rules that block empty or unrelated text parts.
Compare inbox tests before and after converter changes to isolate body-format issues.
Review text links carefully, since long tracking URLs can make the body hard to parse.
Marketer from Email Geeks says autogenerated and edited text can both work, and occasional small mismatches rarely decide placement.
2022-11-04 - Email Geeks
Marketer from Email Geeks says the deliverability concern is a text part that looks like hashbusting, not whether it was written by hand.
2022-11-04 - Email Geeks
The practical recommendation
Yes, the plain text version can affect deliverability, but only as a supporting content and MIME signal. It is not a shortcut around poor sender reputation, weak authentication, high complaints, or messy list acquisition.
My recommendation is simple: keep sending a plain text version, generate it automatically, review it in QA, and reserve manual edits for templates where the generated output is unclear. The best version is the one that is readable, structurally valid, and consistent with the HTML.
If you have to choose between a basic generated text part that is always present and a manually edited text part that people forget, choose the generated one and improve the rules over time.
