Plain text vs HTML cold email

What HubSpot's email tests show, and how to choose a format for cold outreach.

Impact
High
Effort
Low
Updated

For cold email, plain text, or something close to it, is the safer default. It looks like a message from a person, and it avoids the images and tracking code that make an email look like marketing. The best public evidence is HubSpot's A/B tests of marketing email, where the simpler email won every time. No clean plain-text versus HTML test on cold email turned up in the sources below, so run your own.

What HubSpot's tests found

HubSpot tested HTML-rich emails against simpler ones, down to plain text, on its own subscriber lists. Its article, last updated June 13, 2025, reports that in every single A/B test the simpler-designed email won, with statistical significance. Some of its results:

  • Plain text against a version with a GIF: the plain-text email got 42% more clicks (HubSpot).
  • Plain text against an HTML template with images: the HTML version got 51% fewer clicks (HubSpot).
  • A simple HTML template against a heavy one: the simple one got 30% more clicks (HubSpot).

HubSpot also says its HTML and plain-text emails had the same deliverability. It found a lower open rate for HTML anyway, and suggests that image tags and rich templates get flagged as commercial email and sorted out of the main inbox, for example into Gmail's Promotions tab.

Read these results with care. They come from marketing email to opted-in subscribers, not cold outreach. HubSpot's "plain text" still included links and tracking pixels so it could count opens and clicks, and its click gains combine a lower open rate with a lower click-through rate for the HTML versions. The page does not date the individual tests. And in a 2014 survey of over a thousand professionals, HubSpot found nearly two thirds said they preferred HTML and image-based email, yet the simpler emails performed better.

How to do it

  1. Write the first email as plain text: no logo, images, buttons or colors. Use a short text signature with your name, role, company and website.
  2. Use one link at most, and none if you are only asking a question. Every link and image is something a filter can score.
  3. Turn off open tracking. A tracking pixel needs HTML. Instantly's text-only mode sends the email as plain text and stops open tracking, so you will judge the test on replies.
  4. If you must send HTML, keep it simple and well formed, and include a plain-text version. HubSpot says broken tags can get you marked as spam, and Google's guidelines say to format HTML messages according to HTML standards and not to use HTML or CSS to hide content.
  5. Test it yourself. Split one list at random, send the same copy in both formats, and compare human replies. Count carefully: at Sales.co's average human response rate of 0.70%, 500 emails produce about 3 or 4 replies, so small tests cannot detect small differences.

Examples

  • HubSpot ran the tests above on its own email program and published the percentages, including the 42% click gain for plain text over a GIF.
  • Instantly, a cold email platform, offers a text-only setting at the campaign level and a setting to always send the first email as text-only. Its help center notes that text-only sends are not tracked for opens, so choosing the format also means choosing your metric.

Limits: when it backfires

  • Plain text has no room for a product screenshot. If your offer needs a picture, link to a hosted page in a later email, or send it after the prospect replies.
  • Format is a small lever. Sales.co's data ranks who you email first, then whether you reach the inbox, then what the first message says.
  • The law applies to every format. CAN-SPAM requires your valid physical postal address and an opt-out in the message, honored within 10 business days, and it has no exception for business-to-business email.
  • Senders of 5,000 or more messages a day to Gmail must also meet Google's bulk rules, including one-click unsubscribe, which applies to marketing and promotional messages. Check that your sending tool handles this.
  • Brand or compliance teams may require HTML. Then use the simplest template you are allowed, with a plain-text alternative.

Questions people ask

Does HTML send cold email to spam? Not by itself. HubSpot found equal deliverability for properly coded HTML with a plain-text version. What hurts is broken code, heavy images, hidden content and tracking links.

Is plain text better for cold email? It is the better first guess, because it matches how people write to each other and removes things that can trigger filters. HubSpot's tests support simpler email, but they were not run on cold outreach.

Sources

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