Both HTML and plain text emails work. Which one you should use depends entirely on what you're sending and to whom. Cold outreach, transactional receipts, and marketing newsletters each have a different right answer, and running them all through the same format is where most teams end up with deliverability problems they can't explain.
The infrastructure underneath the format determines whether any of it reaches the inbox. Format is one variable inside that system.
What HTML Email and Plain Text Email Actually Are
A plain text email is characters, words, line breaks, and URLs. No styling, no images, no buttons. Every email client renders it. There's nothing to decode, nothing to block, and nothing that can render incorrectly.
An HTML email is a web document embedded in an email. It can include images, branded layouts, buttons, custom fonts, color, and structured formatting. Marketing newsletters, promotional campaigns, and transactional receipts from e-commerce platforms are almost all HTML.
Most email clients send both versions simultaneously as a MIME multipart message: a plain text fallback and an HTML version. The receiving client picks which one to render based on user preferences and client capabilities. When you're deliberately choosing between formats, you're choosing which version to prioritize and how much HTML complexity to build in.
When Plain Text Wins
Cold email outreach
For cold email, plain text is the right default. A cold email is supposed to read like a message from a person, because that's what a well-written cold email is. Heavy HTML formatting signals mass-send to spam filters and to the human reading the message.
Spam filters evaluate HTML emails more aggressively than plain text. HTML introduces image tracking pixels, link redirects, styling attributes, and hidden text that spam filters are trained to scrutinize. A clean plain text email has fewer signals to evaluate, which means less friction at the filter layer.
There's also the inbox clipping issue. Gmail clips messages that exceed roughly 102KB. Most professional cold emails won't hit that limit in plain text. Load an email with images, custom fonts, and a branded header, and you're burning through file size fast. A clipped email hides your tracking pixel, breaks your read receipts, and can hide your unsubscribe link depending on where it sits in the layout.
Plain text cold emails, when sent from properly warmed infrastructure with clean authentication records, consistently outperform heavily branded HTML versions on reply rate. The message reads like it came from a person because it did.
One-to-one business communication
When you're emailing a prospect directly, sending a follow-up, or writing to someone in a real sales conversation, plain text is the right choice. A branded HTML footer and a company logo on a personal outreach email undercut the message. It looks like a template, and the person reading it knows it.
When HTML Wins
Marketing newsletters and promotional campaigns
Subscribers to your newsletter signed up knowing they'd get formatted content from your brand. HTML is the right format here. You need images, layout, section headers, and clear calls to action. A plain text newsletter is technically functional but creates a worse reading experience than subscribers expect.
The sender reputation stakes are also lower on opted-in marketing email than on cold outreach. Your list engaged with you enough to subscribe, so engagement rates tend to be higher, which keeps your reputation healthy even with HTML's additional spam filter exposure.
Transactional emails
Password resets, order confirmations, shipping updates, and invoices should be HTML. These emails carry brand-critical information. A well-formatted receipt is easier to read, easier to archive, and easier to act on than a block of plain text. Recipients expect structure from transactional mail.
Transactional email also benefits from high engagement rates that come with expected, triggered messages. People open order confirmations. That engagement protects your sending reputation even when you're sending formatted HTML.
Re-engagement campaigns
When you're trying to reactivate a list that's gone quiet, a well-designed HTML campaign with clear branding and a direct call to action performs better than plain text. The visual cues help people remember who you are and why they signed up.
What Format Actually Does to Deliverability
Spam filters evaluate hundreds of variables when deciding where to route your email. Format influences a handful of them.
HTML emails carry more payload than plain text. Larger files give spam filters more content to evaluate. Complex HTML with multiple images, external asset loads, and heavy CSS gets scrutinized more than a plain text message.
Image-heavy HTML emails require images to be enabled before the message makes sense. Many email clients block images by default. An email that's a header image and a button is unreadable without images enabled, which hurts engagement metrics and can damage your domain reputation over time.
Link redirects inside HTML emails add another layer of filtering. Many marketing ESPs route links through their own tracking domains. If those tracking domains share infrastructure with senders who have poor reputations, your email inherits some of that friction.
Plain text sidesteps all of these issues. There's no image loading, no external asset, no redirect tracking. The tradeoff is that you lose formatting control and visual brand expression.
What Actually Determines Whether Your Email Lands
Format is a contributing variable in deliverability, not the deciding one. The real determinants are infrastructure.
Domain reputation
Your domain reputation is the primary signal mail providers use to evaluate your sending. Every bounce, spam complaint, and unsubscribe affects it. A domain with strong reputation lands HTML emails in the inbox. A domain with poor reputation filters plain text emails to spam. Format doesn't fix bad domain reputation.
For cold email outreach, this is why secondary sending domains matter. Run cold outreach off your primary business domain and reputation damage from campaigns hits your transactional mail, client correspondence, and invoices. Keep cold email sending on dedicated domains with isolated reputations.
Email warmup
Email warmup builds the sending history that mail providers need to trust a new domain or inbox. A new sending domain hitting inboxes with 50 emails on day one will get flagged, regardless of whether those emails are HTML or plain text. Warmup is a gradual increase in send volume over two to four weeks, with real engagement signals mixed in. Without it, mail providers have no history to evaluate, so they default to suspicion.
Skipping warmup is one of the most common and most expensive mistakes in cold email setup. New domains that go straight into high-volume sending burn fast, sometimes within days.
IP reputation
Your sending IP carries its own reputation score separate from your domain. On shared IPs, other senders affect your deliverability. On dedicated IPs, you control your own history but start with no established trust. Spam filter services like Talos and SenderScore aggregate complaint and bounce data at the IP level. A flagged IP creates deliverability problems regardless of your domain's reputation or your email format.
Authentication: SPF, DKIM, and DMARC
Authentication records tell receiving mail servers that your sending infrastructure is legitimate. SPF lists the servers authorized to send from your domain. DKIM signs your messages so receiving servers can verify they haven't been tampered with in transit. DMARC tells receiving servers what to do when SPF or DKIM checks fail.
Missing or misconfigured authentication is one of the fastest ways to kill email deliverability. Google and Microsoft now require proper authentication for bulk senders, and the threshold keeps dropping. If your DNS records aren't configured correctly, your emails fail at the authentication layer before a spam filter ever evaluates format or content.
Sender reputation and list quality
Your sender reputation is the composite score mail providers assign based on observed behavior over time. High engagement builds it. Bounces, spam complaints, and sudden volume spikes damage it. Keep bounce rates below 2%, ideally below 1% for cold outreach. Verify your lists before importing them to your sequencer. Clean lists protect your reputation whether you're sending HTML or plain text.
The Cold Email Infrastructure Stack
If you're running cold outreach and debating HTML versus plain text, settle the infrastructure question first. Your cold email infrastructure determines whether any emails reach the inbox at all. Format optimization is downstream of that.
A properly configured cold email setup includes secondary sending domains (never your primary business domain), real provider inboxes on Google Workspace or Microsoft 365, SPF and DKIM and DMARC records configured correctly, a completed warmup period before campaign sending begins, and active monitoring of bounce rates and spam complaint rates.
At ScaledMail, we provision and manage this stack. Google Workspace and Microsoft 365 inboxes on dedicated sending domains, with authentication configured correctly and warmup built into the setup process. Continuous monitoring means problems get flagged before they turn into burned domains.
Once your infrastructure is clean, the format question answers itself: plain text for cold outreach, HTML for newsletters and transactional mail. Get the foundation right first. Format choices only matter when your emails are actually reaching the inbox.
