Plain Text vs HTML in Cold Emails: The Data Behind the Debate
There is a debate in cold email circles about whether to send plain text or HTML emails. On one side, people argue that HTML templates look more professional and let you include branding. On the other side, people argue that plain text emails look like personal messages and perform better.
The data settles this debate pretty conclusively: for cold email, plain text wins. Not by a small margin. By a significant, measurable, consistent margin. Here is why, and the few edge cases where HTML might be acceptable.
Why Spam Filters Prefer Plain Text
Spam filters analyze the structure and composition of every email that passes through them. One of the strongest signals they use is whether an email looks like a mass marketing communication or a personal message.
HTML emails contain markup code: div tags, style attributes, image references, table structures, and link formatting. This markup is invisible to the reader but fully visible to the spam filter. And the filter knows that personal emails between two people almost never contain this kind of markup.
When you open a conversation between two colleagues in Gmail and inspect the source, you see minimal formatting. Maybe some basic paragraph tags if they used rich text, but nothing like the complex HTML structure of a marketing template. Spam filters have been trained on billions of examples of both types, and they are very good at distinguishing the two.
Plain text emails, by contrast, contain nothing but text. They look exactly like a message one person typed to another person. There is no structural signal for the spam filter to flag. The email passes the format test cleanly.
This does not mean every HTML email goes to spam. Well-established senders with strong reputations can send HTML marketing emails and reach the inbox consistently. But cold email operates from a position of lower trust. You are emailing someone who does not know you, and your domain is likely newer with less established reputation. Starting from that position, adding HTML formatting is stacking the odds against yourself.
The Tracking Pixel Problem
HTML cold emails almost always include a tracking pixel, a tiny, invisible image that loads when the recipient opens the email. This pixel pings a server and records the open event, giving you open rate data.
Spam filters know about tracking pixels. They have been detecting them for years. The presence of a tracking pixel is one of the clearest signals that an email is a mass communication, because personal emails between individuals do not contain tracking infrastructure.
Beyond spam filtering, tracking pixels create a data quality problem. Apple Mail, which accounts for about 49% of email opens, pre-loads all images including tracking pixels. This means Apple Mail users register as "opened" even if they never actually read your email. Your open rate data is inflated by nearly half, making it unreliable as a performance metric.
When you send plain text cold emails, you naturally avoid the tracking pixel issue because plain text emails cannot contain images. You lose open rate data, but that data was unreliable anyway. You gain better deliverability and cleaner metrics (reply rate, which actually matters).
Link Tracking and Deliverability
Most cold email platforms rewrite your links for click tracking. Instead of pointing directly to your website, the link first goes through a tracking server that records the click before redirecting to your destination.
These tracking redirects are another spam filter signal. The redirect URLs often come from shared domains used by thousands of other senders, some of whom have poor practices. If your click tracking link redirects through a domain with a bad reputation, your email inherits some of that negativity.
In plain text emails, you can include a link, but you should keep it to a single, direct link without tracking. One clean URL to your calendar or website looks natural. Multiple tracked URLs with UTM parameters look like marketing infrastructure.
The tradeoff is real: you lose click tracking data. But for cold email, click data is a vanity metric anyway. The metric that matters is replies. If someone clicks your link but does not reply, you have not moved the needle. If someone replies without clicking any link, you have started a conversation.
What "Plain Text" Actually Means
When cold email experts say "plain text," they mean emails that look and feel like a message you would send from your personal email to a friend or colleague. No images, no styled buttons, no colored backgrounds, no multi-column layouts.
This does not mean you cannot use any formatting at all. Most email clients support basic formatting in what appears to be plain text: line breaks, paragraphs, and even bold or italic text through simple styling. The key is that the email should look like a human typed it, not like a designer built it.
Here is the test: if you showed your cold email to someone without context and asked "is this a personal email or a marketing email?", they should not be able to tell immediately. The moment they see a header image, a colored button, or a multi-section layout, they know it is marketing. Plain text passes this test. HTML templates do not.
The Professionalism Objection
The most common argument for HTML in cold email is professionalism. "A branded template looks more professional and credible," the argument goes. "Plain text looks lazy."
This gets the psychology backwards. In the context of cold email, a branded HTML template does not signal professionalism. It signals mass communication. It tells the recipient "I sent this exact template to hundreds of people today, and you are just one of them."
A plain text email signals the opposite: "I sat down and wrote this to you specifically." Even if the recipient suspects it is a semi-automated outreach (and sophisticated recipients usually do), the plain text format keeps the door open for that perception of personal attention. An HTML template slams it shut.
Think about how you communicate with important people in your professional life. When you email your CEO, a key client, or a business partner, you do not use an HTML template. You type a plain text message. The format itself communicates respect and personal attention. Your cold email should do the same.
When HTML Might Be Acceptable
There are narrow scenarios where HTML in cold email can work, though "acceptable" is a better word than "optimal."
If you are sending to warm leads who have already interacted with your brand (visited your website, downloaded content, attended a webinar), a lightly styled email with your logo and one call-to-action button can work. These recipients already know you, so the marketing format is not as jarring, and your engagement history with them provides some spam filter insulation.
If your product is inherently visual (design tools, visual collaboration, photography services), a single embedded image showing your product in action can add value that text alone cannot convey. But keep the HTML minimal: one image, no template, no footer full of social links.
If you are sending follow-ups to people who have already replied to a plain text initial email, you have established a conversation. At that point, light formatting (like a bulleted list of features they asked about) is acceptable because the recipient has already engaged with you.
In all these cases, the HTML should be minimal. One image at most. No template wrapper. No tracking pixel. No multiple CTAs. The closer your HTML email resembles plain text with one visual addition, the better it will perform.
Setting Up Plain Text in Cold Email Tools
Most cold email platforms default to HTML mode because their rich text editors generate HTML behind the scenes. Even when you type plain text, the platform may be wrapping it in HTML tags.
Check your platform's settings for a plain text or "text only" sending option. Instantly, Smartlead, Lemlist, and Woodpecker all support plain text sending, though the configuration varies.
After setting up plain text mode, send yourself a test email and inspect the source code (in Gmail: click the three dots, then "Show original"). Verify that the email source contains minimal HTML. Some markup is unavoidable (email clients add basic structure), but you should not see complex styling, image tags, or tracking pixel references.
Disable open tracking explicitly. Even in plain text mode, some platforms inject a tracking pixel through a separate mechanism. Turn off open tracking in your campaign settings. You want zero invisible image loads in your outgoing emails.
Disable click tracking for your first-touch emails. You can consider enabling it for follow-ups to warm leads if the data is valuable to you, but for the initial cold email, clean links perform better than tracked redirects.
Measuring Success Without Open Tracking
Without open rate data, how do you know if your emails are performing? The answer is simpler than you think.
Reply rate becomes your primary metric. Did the email generate responses? That is what matters. An email with a 10% reply rate is performing well regardless of whether the open rate was 30% or 60%.
Bounce rate tells you about list quality. If your bounce rate is under 1%, your list is clean. If it is over 2%, you have list quality issues to address.
Inbox placement testing (using seed testing tools) tells you whether your emails are reaching the inbox. This replaces the indirect signal that open rates used to provide.
Meeting booked rate tells you about the full funnel. Replies are good, but meetings booked is the business outcome you care about.
Together, these metrics give you a clearer picture of performance than open rates ever did. You are measuring what actually happens (replies, meetings, deals) rather than a proxy signal (opens) that was never reliable to begin with.
The plain text vs HTML debate is settled by data, not opinion. For cold email, plain text delivers better inbox placement, higher reply rates, and more reliable performance metrics. The small loss in tracking data and visual polish is vastly outweighed by the gain in deliverability and engagement. Send plain text. Track replies. Book meetings.
