Most deliverability conversations start with DNS records and warmup schedules. Those matter, but a perfectly authenticated domain can still land in spam because of how the message itself is built. A logo-heavy HTML template, three tracked links, and a 40-line signature tell a mailbox provider that this looks like marketing mail, not a one-to-one business note. Since Google and Yahoo began enforcing bulk sender requirements in February 2024, and Microsoft extended similar rules to Outlook.com in 2025, message-level signals get more scrutiny, not less.
This guide covers the formatting decisions that affect email deliverability for cold outreach: plain text versus HTML, links, tracking, signatures, and length. It also shows how to enforce these rules automatically, so they hold when you scale beyond what one person can review by hand.
Mailbox providers score messages on sender reputation, authentication, recipient engagement, and content. Content is the only one of the four you control on every single send.
Cold email has a structural problem here. A legitimate one-to-one message from a colleague has a predictable shape: plain paragraphs, no images, at most one link. Marketing mail has a different shape: banners, buttons, multiple tracked links, and tables. When a cold email carries marketing-style structure, filters have less reason to treat it as personal correspondence, and once complaint or low-engagement signals pile up, the domain pays for it.
Formatting also affects the buyer. A VP of operations who receives what looks like a newsletter reads it as a broadcast. A short, unformatted note reads as a person who did their homework. The same choices that help inbox placement tend to help reply rate, which is why this is worth getting right before you touch subject lines. For a separate look at the wording side, see our guide to how to write cold emails that get replies.
The default recommendation for first-touch cold email is plain text, or a minimal HTML email with no images, no buttons, and no custom fonts. Typical mail clients render the latter as plain text anyway.
What to strip out:
- Banner images and logos in the body. Image-heavy messages with little text are a classic spam pattern, and they invite image-blocking on the recipient side. - Buttons and styled calls to action. "Book a demo" as a button is a marketing convention. A plain sentence asking for a conversation is a sales convention. - Multiple fonts, colors, and bold text. One or two bolded phrases at most, ideally zero in the first touch. - Attachments. Never attach files to a cold first touch. Offer to send the material instead, which also gives you a natural reason for the prospect to reply.
An easy test: send the message to a personal Gmail account and to a work Outlook mailbox. If it looks like something a colleague might have typed in thirty seconds, it passes. If it looks designed, cut it back.
Plain text has a second benefit. It renders identically on mobile, where most first opens happen, so you don't debug layout across clients.
Links are the highest-risk element in a cold email. Every URL is a chance to point at a domain with a poor reputation, and each one adds to the "promotional" profile of the message.
A workable standard for the first touch:
1. Zero links in the first email, where you can. End with a question. The reply is the conversion, and it also builds positive engagement history for your sending domain. 2. At most one link in follow-ups, and only when it adds evidence, such as a relevant case study or a short product page. 3. Never use link shorteners. Public shorteners such as bit.ly are heavily abused by spammers and are widely treated with suspicion. Link directly to a real page. 4. Match link domains to your brand. A link to a domain unrelated to your sender identity looks like redirection. If your link domain and sending domain are different, they should be clearly related and both properly configured. 5. No raw IP addresses or long parameter strings in URLs.
The same discipline applies to your calendar link. Many teams paste a scheduling URL into the first email, which converts a soft ask into a commitment and adds a link at the worst possible moment. Ask "worth a quick conversation?" first, and send the calendar link only after a positive reply. Our follow-up email strategy shows where in a sequence links and assets fit best.
Open tracking works by embedding a tiny image, a tracking pixel, and often routes it through a tracking domain shared with other customers of your sending tool. Three problems follow:
- The data is unreliable. Apple Mail Privacy Protection preloads images regardless of whether the person read the email, and many security gateways do the same. Open rates inflate and stop reflecting interest. - It adds a remote image request to a message that otherwise has none, which changes how the message is classified. - Shared tracking domains inherit shared reputation. If other senders on the same custom or default tracking domain have burned it, your links and pixel carry that history.
For cold outreach, measure what matters: replies, positive replies, and booked meetings. These are unambiguous, and they don't depend on a pixel. If you do need click tracking for a specific asset, use a dedicated custom tracking subdomain on your own domain, with proper DNS records and warmup, and apply it only where the data changes a decision.
This is also why our cold email deliverability audit framework treats open rate as a weak signal and looks at inbox placement and bounce data instead.
Signatures are a frequent source of accidental formatting problems. Corporate signatures often include a logo image, social icons, a legal disclaimer, and a banner promoting a webinar. Each of these adds images, links, and length to a message you are trying to keep sparse.
A cold-outreach signature should include:
- Name and title - Company name (plain text) - One contact detail, if any
Leave out image logos, social icon rows, promotional banners, and long confidentiality notices. Your compliance obligations still apply. Include a physical address where CAN-SPAM requires it and provide a clear way to opt out, in line with the rules covered in our cold email compliance guide. A plain sentence such as "If this isn't relevant, tell me and I'll stop" satisfies the spirit of the requirement and reads like a human wrote it.
Length is a formatting decision, too. Cold emails between 50 and 125 words tend to perform best in most published outbound benchmarks, and they give filters less content to score. A workable structure:
1. One line of relevance: why this person, why now. 2. One or two lines of value: a specific outcome, ideally with a number. 3. One question: low-friction, answerable in a sentence.
Avoid all-caps words, strings of exclamation marks, and phrases that read like ad copy ("limited time," "act now," "guaranteed"). Words on a spam-trigger list matter less than they once did, but the underlying pattern, urgency plus a promise plus a link, is still a reliable negative signal.
The numbers below are illustrative. Replace them with your own test data.
Before: an HTML template with a logo, a two-color header, three tracked links (website, case study, calendar), open tracking on, a 12-line signature with social icons, and 190 words of body copy.
After: plain text, 70 words, no links in touch one, open tracking off, a four-line signature, and a single question at the end.
Run both versions as an A/B test across matched segments, with the same sending domains and the same lead source, and compare inbox placement (via a seed list) and positive reply rate over two weeks. Teams that run this test often find the simpler version places more consistently and replies at a higher rate, but your audience and sending infrastructure will decide. Our cold email A/B testing framework explains how to structure the test so the result is statistically meaningful.
Rules like these are simple. Enforcing them across thousands of sends and a rotating set of mailboxes is where teams slip. An SDR in a hurry pastes a tracked calendar link. A new template inherits the corporate signature. Someone switches on open tracking "just to see."
Automated prospecting workflows remove that drift. Formatting policy becomes a system setting instead of a habit: plain-text templates by default, link limits per touch, tracking off on cold sends, and a standard signature applied to every mailbox. This is one of the practical differences between an SDR replacement workflow and a manual process. The system applies the same standard on the ten-thousandth send as on the first, and it does so while personalizing each message from researched prospect data.
Formatting is the cheapest deliverability lever you have. Send plain text, keep the first touch link-free, turn off open tracking, trim the signature, and hold the body to a short note with a single question. None of this requires new infrastructure. It requires deciding on a standard and applying it consistently.
OnyxSend builds these defaults into its automated cold email workflows, so every sequence goes out with plain-text formatting, link limits, and tracking-off settings already in place, alongside ICP-scored targeting and per-mailbox volume controls. See our pricing or start a trial to test a formatted sequence against your own target list.