Cold Email: HTML vs Plain Text — Which Gets More Replies?
By Puzzle Inbox Team · Apr 24, 2026 · 7 min read
Plain text cold emails consistently outperform HTML. Here is the deliverability, reply rate, and trust data across thousands of campaigns.
The HTML vs Plain Text Debate Is Over for Cold Email
Plain text wins. Not by a small margin — by a significant one. Across thousands of cold email campaigns we have analyzed, plain text emails outperform HTML on every metric that matters: inbox placement, reply rate, and trust perception. The debate about "should I use HTML in cold email" has a clear answer for 2026: only if you have a specific reason, and never by default.
The Data
Analyzing cold email campaigns across infrastructure types:
- Plain text reply rate: 4.1% average
- HTML reply rate (basic): 3.0% average
- HTML reply rate (designed/template): 1.8% average
- Plain text inbox placement: 88% average
- HTML inbox placement (basic): 78% average
- HTML inbox placement (designed): 62% average
The gap between plain text and designed HTML is massive — 2x reply rate difference. Designed HTML cold emails get classified as marketing/promotional by Gmail's Promotions tab algorithm, which kills deliverability.
Why Plain Text Wins for Cold Email
1. Looks Like a Real Email
Cold email mimics a personal email sent by one human to another. Plain text matches that format. HTML templates with headers, images, buttons, and footers look like marketing emails — because they are what marketing emails look like.
2. Avoids the Promotions Tab
Gmail Promotions tab algorithm specifically filters HTML marketing emails. Plain text emails are much less likely to land in Promotions. For cold email to be effective, it needs to be in the primary inbox — not Promotions, not spam.
3. No Image Load Warnings
Gmail blocks images in HTML emails by default for unknown senders. Prospects see "images not displayed" warnings that immediately flag your email as untrusted. Plain text has no images to block.
4. Faster to Read
Plain text loads instantly. No rendering delays, no layout issues across email clients. On mobile especially, plain text is dramatically faster to parse.
5. Harder to Fingerprint
Spam filters use HTML structure as a fingerprint. Identical HTML templates across thousands of emails trigger bulk mailer detection. Plain text has no template fingerprint to match.
When HTML Makes Sense for Cold Email
Narrow cases:
- Linked case study email (later in sequence): Email 3 or 4 in a sequence where you are sharing a case study link — light HTML with one hyperlink can work
- Rich media content pitches: If you are pitching journalists and need to show visual assets — but use attachments, not embedded images
- E-commerce product pitches: Very specific B2B e-commerce cases where product image matters
Even in these cases, minimal HTML (one link, no images, no design) outperforms designed templates.
How to Write Cold Email in Plain Text
- Turn off HTML formatting in your sending platform
- Use plain paragraph breaks — no headings, no lists with bullets, no bold/italic formatting that relies on HTML
- Write conversationally — as if typing a personal email to a colleague
- One link maximum (in follow-ups, not first emails) — plain text hyperlinks render fine
- Simple signature — name, title, company, phone (no logo, no social icons)
The Hybrid Approach
Some cold email operators send "multipart" emails that include both plain text and HTML versions. The email client picks which to display. For cold email, even this is unnecessary — sending only plain text is cleaner and avoids any risk of the HTML version triggering filters.