The plain text versus HTML question comes up because of a persistent belief that plain text emails get better deliverability. They do not, at least not for the reason people think. Filters do not reward the absence of HTML.
What is true is narrower and more useful: emails that are mostly image with almost no text score badly, links that do not match their anchor text score badly, and messages with no text alternative at all score slightly badly. Plain text emails avoid all three by construction, which is why the correlation exists and why the causal story is wrong.
What you are actually choosing between
Almost every marketing email is sent as multipart/alternative: one message carrying both an HTML part and a plain text part, with the recipient's client picking. So the real question is not which format to send. It is what the HTML part should look like, and whether you are paying attention to the text part.
The answer to the second is that most senders are not. Auto-generated text parts derived from image-heavy HTML are often close to empty, which is exactly the signal that hurts. Read yours.
When plain text genuinely wins
Anything meant to prompt a reply. Sales follow-ups, founder notes, "how is it going?" check-ins. A styled template signals broadcast, and people do not reply to broadcasts. This is the strongest case for plain text and it is a psychological one, not a technical one.
B2B into corporate inboxes. Security gateways scrutinise heavy HTML, rewrite links and strip elements. Simple messages pass through more cleanly. See B2B email marketing.
Cold outreach. Same reasoning, plus a template makes it obvious the message went to hundreds of people.
Anything from a person, about a specific thing. If the email would look strange with a header image, do not add one.
Accessibility fallback and text-only clients. Which is every email, via the text part.
When HTML wins
Anything with products in it. People buy things they can see. An ecommerce campaign in plain text leaves money on the table, and no amount of deliverability folklore compensates.
Anything with structure. Multiple items, comparisons, a table of data. Plain text handles hierarchy badly.
Anything where brand recognition is part of the job. A newsletter people have subscribed to for years benefits from looking like itself.
Anything where you need click data by element. Plain text gives you clicks; HTML tells you which of three buttons.
The middle ground most senders should use
The format that performs best for many senders is neither: lightly styled HTML that looks like a letter. One column, real text, a couple of links, brand colour on the button, no hero image, no three-column footer.
It gets HTML's tracking and structure, keeps a high text-to-image ratio, renders predictably in every client including Outlook, survives dark mode without heroics, and reads as though a person wrote it. If you are redesigning a template, this is the direction worth trying.
The things that actually affect deliverability
Since this is the question underneath the question:
- Text-to-image ratio. An email that is one large image with a line of alt text is a classic spam pattern. Keep real text in real text.
- Link and domain reputation. Links to a domain with a bad reputation hurt regardless of format. So do link shorteners, which obscure the destination.
- Mismatched anchor text. Anchor text reading
example.comwhile the href points elsewhere is a phishing pattern and is scored as one. - Authentication. SPF, DKIM and DMARC matter more than every formatting decision combined.
- Engagement. Whether people open, click and do not complain outweighs everything else.
- A missing or empty text part. Cheap to fix, and worth checking.
Format is not on that list except through the text-to-image ratio. If your deliverability is poor, look at why emails go to spam rather than at your template.
Practical rules
- Always send both parts, and read the text part before you ship.
- Keep a healthy proportion of real text in the HTML.
- Use plain text for anything expecting a reply.
- Use HTML for anything selling something visual.
- Test both parts — some clients, and many watch apps, show the text version.
Frequently asked questions
Do plain text emails have better deliverability than HTML?
Not inherently. The perception comes from plain text avoiding three real problems — image-heavy layouts with little text, mismatched links, and missing text parts. Well-built HTML with a healthy text ratio performs the same.
Should I send both plain text and HTML?
Yes. Nearly all platforms send multipart/alternative by default. The part worth your attention is the auto-generated text version, which is often nearly empty for image-led designs and is what some clients and screen readers actually display.
Which converts better?
It depends on the ask. Plain text converts better for replies and for anything personal. HTML converts better for anything visual or with several options, because people buy what they can see.
Does image-heavy email hurt deliverability?
Yes, when there is little real text alongside. Filters cannot read images, so a message that is one large graphic looks like an attempt to hide content. Keep meaningful copy as text and give every image proper alt text.
