Cold Email Format: Structure, Headers, Video

What is a cold email, and how is it different from spam?

A cold email is a one-to-one message to someone who has no prior relationship with you. Usually that's a named person at a business you've researched. Having no relationship isn't what makes a message spam. The difference is relevance, a real sender identity and an easy way to opt out. Mailbox providers judge cold email the same way they judge any other mail: by authentication, by complaint rates and by how recipients react. Gmail's sender guidelines ask senders to keep the user-reported spam rate below 0.3%. Anyone sending close to 5,000 messages a day to personal Gmail accounts counts as a bulk sender and has extra requirements to meet. A cold email also isn't a newsletter. It goes to one person, talks about their situation and asks for one thing. That's why the format matters. The structure, headers and body have to read like a message from a person, because with EmailFlow OS that's what it is: each version goes out from the customer's own inbox, through their own Brevo account and sending domain, not through a shared platform address.

What does a good cold email format look like?

Strip out the fashions and a working cold email format has six parts, in this order. Each part has a job. Anything that doesn't do one of those jobs is just extra weight for the reader.

1. 1 Subject line: short, specific, no bait. The US CAN-SPAM Act prohibits subject lines that mislead about what's in the message.
2. 2 Preview text: the snippet inbox lists show next to the subject. If you leave it empty, the client shows whatever text comes first, and that can be 'View in browser'.
3. 3 Opener: one sentence on why you're writing to this particular person, like their role, something they published or a change at their company.
4. 4 Relevance: two or three sentences that connect their situation to what you do. No feature lists.
5. 5 One ask: a single question or next step. Two asks split the reply.
6. 6 Signature and opt-out: full name, company, a postal address where the law requires one, and a plain way to decline further mail.

Here's what doesn't work: long introductions about your company, attachments from a sender the recipient doesn't know, and signatures built from five images. Subject lines are a discipline of their own. Our sales email subject lines guide has examples for cold messages and follow-ups.

Which email headers does a cold email need?

The part of the format nobody sees is the header block, defined in RFC 5322. A lot of cold email breaks there. Check these headers before your first send:

• From: a real person's name and an address on your own sending domain. Not a no-reply mailbox.
• Reply-To: leave it out, or set it to the same mailbox. A Reply-To that doesn't match the From address is a classic phishing pattern.
• Message-ID: unique for every message. Follow-ups reference it in their In-Reply-To and References headers, which is how clients thread them.
• List-Unsubscribe plus List-Unsubscribe-Post: List-Unsubscribe=One-Click. This is the one-click mechanism from RFC 8058, and Gmail and Yahoo require it on promotional mail from bulk senders.
• DKIM-Signature: added by the sending service and checked against a public key published under your domain, as specified in RFC 6376.

Threading only works if a follow-up keeps the original Message-ID chain and the original subject. A new subject line or a fresh message starts a new conversation in most clients. We cover timing and send limits in our article on cold email follow-up timing and threading.

Should a cold email be plain text or HTML?

Send both, in the same message. The MIME type multipart/alternative, defined in RFC 2046, carries a text/plain part and a text/html part, and the recipient's client shows whichever one it can display. A message with HTML and no text part looks like a template to filters and displays badly in text-only clients. Keep the HTML close to plain text: one column, system fonts, no background images, no heavy layout. There are two concrete limits to know. First, Gmail clips messages whose HTML goes over about 102 KB and hides the rest behind a 'View entire message' link. That can hide your signature and your opt-out link. Second, image-only emails, where the whole message is one graphic, give filters no text to read. They also leave the reader with nothing if images are blocked, which is the default setting in some desktop clients. Adding alt text to every image helps in both cases. Newsletter templates with banner headers, several buttons and a row of social icons don't work either. They look like bulk mail before anyone reads a word.

How do you put a video into a cold email?

You can't count on a video playing inside an email. The HTML5 video tag works in a few clients, most notably Apple Mail, but Gmail and Outlook won't play it. Attaching the video file doesn't work either: Gmail caps attachments at 25 MB, and a large attachment from a stranger is exactly what filters distrust. So in a cold email, video means a visual in the body that links to wherever the video plays, plus text that still makes sense if the image never loads.

The harder problem is personalisation, and that's the part EmailFlow OS handles. You record one video and upload it to EmailFlow OS, connect your Brevo account and sending domain, and import your prospect list into EmailFlow OS. EmailFlow OS then personalises that single recording for each recipient, not each company, so two people at the same firm get two different versions. Each version goes out from your own inbox through your own Brevo account and domain. Our walkthrough of personalised video cold outreach with EmailFlow OS shows how this fits into a campaign. Keep the written part short: the video makes the pitch, and the text gives the context and the ask.

Why does the sending domain affect how a cold email is received?

The receiving server looks at your domain before it looks at your copy. Three DNS records decide how it treats your From address:

• SPF (RFC 7208): a TXT record listing the servers allowed to send mail for your domain. It's limited to 10 DNS lookups, and going over that makes SPF fail with a permerror.
• DKIM (RFC 6376): a public key in DNS that receivers use to verify the signature your sending service adds to each message.
• DMARC (RFC 7489): a TXT record at _dmarc on your domain that tells receivers what to do when SPF or DKIM doesn't align with the From domain. p=none only monitors, while p=quarantine and p=reject enforce.

Gmail and Yahoo require bulk senders to have SPF, DKIM and a DMARC record of at least p=none. EmailFlow OS sends through your own Brevo account and your own sending domain, so those records and the reputation they build stay under your control. You publish them in your own DNS, following Brevo's instructions. Where a message gets filed is still the receiving server's decision, not ours or yours. A new domain needs a gradual ramp-up before you send at volume, and our email warm-up guide covers how that works. A common mistake is sending cold mail from your main company domain. Then a bad week also drags down the reputation your invoices and support replies depend on.

What do EU rules require from a cold email?

This section explains the rules. It isn't legal advice, and whether a campaign meets them depends on how you run it. Under the GDPR, using a prospect's business email address for outreach needs a lawful basis. That's often argued as legitimate interest under Article 6(1)(f), which calls for a documented balancing test. If you didn't collect the data from the person directly, Article 14 says you have to tell them where it came from, and Article 14(3)(b) sets the deadline: no later than your first message if you use the data to contact them. Under Article 21(3), once someone objects to direct marketing, you have to stop. National law can be stricter. In Germany, §7(2) no. 2 UWG requires prior express consent for advertising by email, and that covers business recipients too. For the email itself, this means an identifiable sender, the source of the data or a link to your privacy notice, and an opt-out you honour from the first reply onward. Importing your prospect list into EmailFlow OS doesn't change any of this. Establishing the legal basis is your job.

Questions people ask

? How long should a cold email be?

Short enough to read on a phone without scrolling: a one-sentence opener, two or three sentences on why it's relevant, and one ask. That's far shorter than a newsletter. If there's video in the email, the text can be even shorter, because the recording carries the explanation. The text only needs to give the context and make the ask.

? Should a cold email contain links?

Use one link, or none. Every link is a domain the filter checks, and public URL shorteners share their reputation with everyone else who uses them. If you do include a link, it should point to a domain you control, and your plain-text part should show the same URL as the HTML part, so both versions of the multipart/alternative message match.

? Is a video cold email a different email format?

No. It uses the same RFC 5322 headers, the same multipart/alternative structure and the same SPF, DKIM and DMARC checks as a text-only cold email. The difference is in the body: a visual that links to the video, with text that works without it. With EmailFlow OS, each recipient gets their own version of your single recording, sent from your own inbox.

? What format should a cold email follow-up use?

Reply in the same thread instead of starting a new one. Keep the subject with the 'Re:' prefix, and make sure the In-Reply-To and References headers point to the original Message-ID. Clients like Gmail group messages by those headers and the subject. A follow-up with a new subject line shows up as a separate, unrelated email.