Plain text vs HTML email, which format to use for cold email

A rep spends an hour building a branded HTML email. Logo in the header, colored CTA button, custom font. He sends it to 200 prospects and gets three replies. The next morning he fires off a two-line note from the same inbox, no design, no images, just text. Fourteen replies.

Format changes how an email looks to a spam filter and to the person reading it. A designed template reads as marketing. A plain note reads as a person. That difference decides whether your message gets a reply or gets archived.

In this article, I will give you a clear rule for plain text vs html email in cold outreach, and show you exactly when it makes sense to break that rule. I will also cover what spam filters actually check inside your HTML, how open tracking forces a format decision you might not realize you are making, and a way to keep your emails light while still sending prospects a rich, visual experience through a landing page.

By the end, you will know which format to default to, which signals to avoid in your HTML, and how to test the decision instead of guessing at it.

What plain text and HTML email mean

A plain text email is a message with no formatting, no images, and no buttons. An HTML email uses code to add design elements like colors, layouts, hosted images, and clickable buttons.

In practice, most email tools send a multipart MIME message that bundles both an HTML part and a plain text part together. This structure allows a single email to carry two or more distinct body parts, separated by a boundary delimiter string. The recipient’s client renders the last supported part (typically HTML) and falls back to plain text if HTML is unsupported.

When outreach practitioners say “plain text email,” they usually mean an email with no visual design. No header image, no colored CTA button, no multi-column layout. It looks like something you would type to a colleague in Gmail. That simplicity is a feature, and it has a direct effect on email deliverability.

Plain text vs HTML email compared

The table below breaks down the practical differences that matter for outreach.

The pattern is clear. Plain text removes variables. HTML adds them. For cold email, where you have no prior relationship with the reader, fewer variables means fewer things that can go wrong between your send and their inbox.

Why cold email leans plain text

Cold email works when it reads like one person writing to another. For cold outreach specifically, brand consistency matters less than perceived authenticity. Your goal is to sound like a person, not a company.

A polished HTML template does the opposite. A templated HTML layout signals “marketing send” to both the recipient and to filters trained on bulk-mail patterns. The moment a prospect sees a banner image and a styled button, they mentally file the message under “promotion” and move on.

Plain text also has fewer elements that can break. There is no CSS that renders differently in Outlook versus Apple Mail. There is no image that loads slowly on mobile. The message arrives the same way everywhere, which means you spend less time debugging and more time writing copy that earns a reply.

Think about how you write to a colleague. You open a compose window, type a few lines, and hit send. That is the format cold email should mimic.

What spam filters look at in an HTML email

Spam filters parse every element in your HTML. The more elements you add, the more signals they evaluate. Here is what raises flags:

• •

  Broken or bloated code from drag-and-drop builders that produce nested tables and unused tags

• •

  Image-heavy layouts with little actual text, a pattern spammers use to hide content from text-based scanners

• •

  Many links, link shorteners, or links pointing to domains that do not match your sending domain

• •

  Hidden text, like white text on a white background or elements set to display:none

• •

  Missing SPF, DKIM, or DMARC authentication on the sending domain

Content signals that filters weigh include spam-keyword density, excessive HTML-to-text ratio, missing plain-text alternative part, embedded URLs on blocklists, mismatched anchor text and link destination, excessive image use with minimal text, and broken or malformed HTML.

Using images in cold emails is possible, but every image you add is another signal for filters to score. The same goes for language. Certain phrases carry weight with filters, so review common spam trigger words before you launch.

A plain text email sidesteps most of these signals by default. There is no code to break, no image ratio to manage, and no hidden elements to flag.

Open tracking and the format question

Open tracking works by embedding a tiny invisible image in the HTML part of an email. When the recipient’s client loads that image, the sender’s system registers an open.

That means a truly plain text email cannot track opens. Plain text emails do not contain images, so there is nowhere to place a tracking pixel.

This creates a trade-off. Tracking gives you data on who opened your message, but it adds an HTML element to every email you send. That element is one more thing filters can inspect, and privacy tools like Apple Mail Privacy Protection can inflate or block the signal entirely. If you want to learn more about what tracking can and cannot tell you, read how to see if someone read your email.

My recommendation: for first touches, consider turning open tracking off entirely. The reply is the metric that matters most at that stage. If you keep tracking on, set up a custom tracking domain so the tracking pixel loads from your own domain instead of a shared one. That reduces the deliverability risk.

When HTML earns its place in outreach

Plain text is the default, but there are moments where light HTML makes sense:

• •

  A professional email signature with your name, title, and a small logo

• •

  A follow-up to a prospect who already clicked a link or replied, where a visual element adds context

• •

  A nurture email to a warm lead who has opted in and expects richer content

The key word is “light.” If you use HTML in outreach, keep it minimal. One link. No hosted images except a small signature logo if needed. Simple text styling like bold for a single phrase, nothing more. The email should still look like a message from a person, not a campaign from a marketing team.

The moment you add a second image, a colored background, or a multi-column layout, you cross the line from personal note to promotional send. Stay on the right side of that line.

Move the visuals to a landing page

Here is the move most teams miss. Instead of cramming visuals into the email body, keep the email plain and link to a personalized landing page.

The landing page holds the video walkthrough, the customer logos, the product screenshots, and the tailored copy. The email stays lightweight. Filters see a simple message with one link. The prospect clicks through and gets the full visual story.

This approach gives you the best of both worlds. Your email lands in the inbox because it looks like a personal note. Your landing page delivers the rich experience that a designed email tries (and often fails) to provide.

You can personalize the landing page with the prospect’s name, company, and relevant details so it feels built for them, not pulled from a template library.

How to test which format lands

Do not guess. Test.

1. 1.

   Write the same copy in two versions: one plain text, one with light HTML formatting.

2. 2.

   Run seed tests to check inbox placement for each version before you send to real prospects.

3. 3.

   Send both versions to a segment of your list and compare reply rates over the same time window.

4. 4.

   Change one variable at a time. If you change the format and the copy simultaneously, you will not know which one moved the needle.

Reply rate is the metric that decides the winner, not open rate. Opens are noisy. Replies are signal.

How to send plain text cold email in lemlist

Write your email in the lemlist editor without adding images or design elements. The result is a clean, text-only message that looks like it came from a regular inbox. If you ever need to insert custom HTML for a specific use case, switch to the HTML code view inside the editor.

Disable open tracking and click tracking at the campaign level when you want a fully plain send. If you prefer to keep tracking on, set up a custom tracking domain in your account so the pixel loads from your own domain.

To share visuals without weighing down the email, add a personalized landing page to an email step through “Custom media.” The landing page can include logos, video, text, and variables like {{firstName}}, so each prospect sees a page built for them.

A/B test a plain version and a lightly formatted version of the same step. lemlist uses reply rate to decide the winner, which is the right metric for cold outreach.

Before you send anything, warm up your mailboxes with lemwarm. A warmed inbox with a healthy sender reputation is the foundation. Format choices matter, but they matter less than sending from a domain that filters already trust.

Final takeaway

Plain text is the safer default for cold email because it looks personal, travels light through filters, and renders the same everywhere. Use HTML only when you have a clear reason, like a signature or a follow-up to an engaged prospect, and keep it minimal. Move the heavy visuals to a personalized landing page so the email stays clean and the prospect still gets the full story.

Build your first signal-based sequence in lemlist.