Plain Text vs Designed Emails: What the Numbers Say

A short email from the founder beats a polished promotion one week. A product grid beats a letter the next. Both results can be genuine. Email format changes how people read, browse and respond, but it does not work independently of the offer, audience or reason for sending.

There is no dependable universal percentage by which plain text outperforms designed email. Published comparisons often bundle design changes with different copy, link counts or sender names. For a small business, the useful numbers come from a controlled comparison tied to sales, enquiries or replies. Here is how to interpret those numbers and choose a sensible starting format.

First, define what you are comparing

Marketers often call any email without a banner “plain text”. Technically, that is not necessarily true. There are three practical categories:

• True plain text: no HTML formatting, embedded images or styled buttons. Links appear as text URLs.
• Plain-looking HTML: simple paragraphs, perhaps a signature and one linked phrase, built using HTML. It can still contain a tracking pixel.
• Designed HTML: a visible layout with elements such as product photographs, branded headers, buttons and multiple content blocks.

This distinction matters when evaluating results. True plain text cannot contain an image-based open-tracking pixel, so its measured open rate is not comparable with an HTML version. Many supposed “plain text versus HTML” tests actually compare two HTML layouts.

For most businesses, that is the more useful test anyway: a simple, letter-like layout against a designed template. You can change the presentation without rebuilding your sending setup.

What the numbers can actually tell you

Do not assume the version with the highest open rate is the winner. Recipients usually encounter the subject line, sender name and preview text before the body design. Privacy features, image blocking and automated image loading also make open tracking an imperfect measure of human attention.

Clicks are closer to action, but they still need interpretation. Security scanners can trigger tracked links, and a click does not necessarily indicate buying intent. Use your platform’s bot filtering where available, then check outcomes on your website or in your sales system.

A worked example, not an industry benchmark

Suppose a shop randomly splits an audience and sends the same offer in two formats. The following figures are illustrative, not results from a published study. Each version reaches 5,000 delivered emails, and both use the same seven-day sales attribution window.

The designed version generated 25% more unique clickers: 250 versus 200. That is a one-percentage-point increase in click rate, not a 25-percentage-point increase. Yet the plain-looking version produced slightly more attributed revenue.

Neither result justifies a sweeping conclusion. The revenue gap is £50 across 5,000 delivered emails per version, and the order counts are small. A handful of purchases could reverse the ranking. The defensible reading is that the designed email attracted more clicks, while the commercial result remains uncertain.

A format that earns more clicks is not automatically a format that earns more money.

Where each format earns its place

Use plain-looking emails for one focused decision

A letter-like layout is a strong starting point when you want readers to consider one argument and take one action. Examples include a consultant inviting prospects to book a call, a founder explaining a price change, or a course creator answering a common objection.

The practical advantage is focus. Readers have fewer competing routes, and the copy can move directly from problem to explanation to next step. Start with a recognisable situation, use short paragraphs, and make the request explicit: “Reply with your biggest bookkeeping headache” is more useful than “Let us know your thoughts”.

Do not confuse simplicity with simulated intimacy. A bulk campaign should not pretend to be an individual follow-up. Keep the sender identity clear and retain required unsubscribe information.

Use designed emails when seeing helps people choose

Design earns its space when images or structure reduce the work of deciding. A furniture shop can show scale, colour and shape faster than it can describe them. A restaurant can separate booking details from menu highlights. A retailer with three distinct offers can make each route easy to scan.

The strongest designed emails are not necessarily elaborate. One useful photograph, a clear price and a readable button may do the job. Avoid putting essential information only inside images; include live text, meaningful alternative text and a layout that remains usable when images are blocked.

Run a test that answers one question

A comparison between a 100-word founder note and a 600-word catalogue tests more than design. That can be a valid comparison of campaign approaches, but it cannot isolate the effect of formatting.

1. Choose one primary outcome. Use revenue per delivered email for a sales campaign, qualified enquiries for a service offer, or meaningful replies for a feedback request.
2. Randomise comparable recipients. Split the eligible audience randomly. Do not send one format to recent customers and the other to inactive subscribers.
3. Hold the surrounding variables steady. Keep the sender, subject line, preview text, offer, timing and destination consistent. Preserve the core copy and call to action when testing layout.
4. Set the measurement window in advance. For example, count orders within seven days using the same attribution method for both versions. Avoid judging one after 24 hours and the other after a week.
5. Check the guardrails. Review unsubscribes, complaints, delivery and mobile rendering alongside the primary result.

If testing layout, use the same underlying template infrastructure where possible. A broken button, missing tracking parameter or unusually large file introduces a technical difference that can swamp the presentation question.

Small lists need patience, not bigger claims

With 500 delivered emails per version and a 2% conversion rate, you would expect roughly ten conversions in each group. A result of 12 versus eight looks like a 50% lift, but it represents only four additional conversions. That is a fragile basis for changing every campaign.

There is no universal minimum sample size. It depends on your baseline conversion rate, the improvement worth detecting and the level of statistical confidence you require. Use a sample-size calculator before testing when you have enough volume, rather than declaring a winner as soon as one version pulls ahead.

For smaller lists, repeat the randomised comparison across several comparable sends and examine whether the pattern persists. Keep seasonal promotions separate from routine newsletters, and avoid treating repeated sends to the same people as entirely independent evidence.

Count production cost as well as sales

A format can be commercially useful without a measurable conversion advantage. Suppose a designed campaign takes three hours to produce and a simple version takes 45 minutes. At an illustrative internal cost of £40 an hour, the simpler version saves £90 per send.

If revenue and customer experience are effectively similar, that saving matters. If a reusable designed template takes only ten minutes longer, the calculation changes. Compare incremental gross profit with production cost, not just total revenue with hours spent.

Conclusion: choose for the job, then measure

Start with plain-looking HTML for a focused message and designed HTML when visual browsing helps the reader. Test against a business outcome, keep the comparison fair and resist dramatic claims from small differences. The best format is the one that repeatedly earns its place in your own programme.