Cold email deliverability: how to reach the inbox in outreach

In cold outreach, you write to people who asked for nothing, who do not know you, and who may never open your message. From a spam filter's point of view, that is exactly the profile of a sender to watch. Cold email is not a special use case of deliverability: it is its hardest test. Here is how to get through it without burning your domain.

Why cold email is the hardest case

Deliverability relies on engagement signals: opens, replies, spam rescues. A newsletter addresses people who subscribed, so who interact. A transactional email is expected. Cold outreach, by contrast, stacks every handicap: the recipient never interacted with you, rarely opens, replies even more rarely, and may click "Report as spam" rather than "Unsubscribe".

The result: the ratio of negative to positive signals is structurally unfavorable. Where a newsletter tolerates a few missteps, a poorly prepared cold email degrades reputation in a handful of sends. The whole discipline consists in offsetting this engagement deficit with technical rigor and a ruthless selection of recipients.

The technical foundation, before the first send

Isolate on a dedicated subdomain

This is the most important and most often neglected decision. Send your outreach from a separate subdomain, such as contact.yourdomain.com, never from the domain that carries your customer emails and invoices. If outreach goes wrong, the main domain stays intact. Each subdomain needs its own authentication, distinct from the root domain.

Authenticate cleanly

SPF, DKIM and DMARC are non-negotiable, and the subdomain needs its own configuration. Without valid authentication, no warm-up and no brilliant copy will save your sends. The full procedure is in our SPF, DKIM, DMARC guide.

Warm up every inbox

A brand-new address that starts prospecting is the riskiest scenario there is. Every inbox must go through a gradual ramp-up, paired with real engagement signals, before the first cold email. Count on about three weeks, as detailed in our 21-day warm-up method. And warm-up does not stop at the first commercial send: it continues in the background, to offset the engagement deficit of outreach.

Realistic volumes

The classic mistake is to think in total volume rather than volume per inbox. Providers judge each address and each domain. The table below gives cautious orders of magnitude for an inbox dedicated to outreach, to adapt to your results.

The last point is the structuring principle: to send more, you multiply sending inboxes rather than the load of a single one. Beware, though, multiplying inboxes is not a trick to bypass the filters. Every inbox must be legitimate, warmed up, tied to a real person. Account farms are spotted and penalized.

List quality outweighs the text

A clumsy subject line costs you a few replies. A dirty list costs you your domain. The hierarchy is clear-cut.

• Verify addresses before sending: a hard bounce signals a sender who does not know their recipients.
• Avoid generic addresses (contact@, info@, admin@): low engagement, high complaint probability, sometimes spam traps.
• Beware of catch-all domains: they accept everything, so never bounce, and hide the poor quality of the list.
• Do not buy lists and do not scrape the web indiscriminately: it is the fastest path to spam traps.
• Target narrowly: 200 relevant recipients beat 2,000 approximate ones, including for deliverability.

Write an email that looks like an email

A cold email must look like a message written by a person, not a marketing campaign. This is not a matter of style, it is a matter of broadcast signals: filters spot the markers of mass sending.

• Plain text, little or no HTML, no images, no flashy call-to-action button.
• One link at most, pointing to a domain consistent with the sender. Zero opaque redirects.
• A real signature, a named and stable sender address, never a disposable one that changes with each campaign.
• Personalization that prompts a reply: the reply is the most powerful positive signal in outreach.
• A clear unsubscribe line, even in B2B. It turns potential complaints into simple opt-outs.

The case of open tracking

Many tools insert a tracking pixel and rewrite links through a tracking domain shared with hundreds of other clients. If that domain is poorly rated, you inherit the problem. Two options: disable open tracking in outreach, or set up a custom tracking domain. Open tracking has in any case become unreliable since the privacy protections of mailbox providers.

The legal framework (France and the EU)

Deliverability and compliance reinforce each other: a legally built list is also a list that generates fewer complaints. In France, the CNIL clearly distinguishes two regimes.

• In B2C, to a personal address, prior consent is required. No opt-in, no send.
• In B2B, to a professional address, outreach is possible without prior consent provided the message relates to the role of the person contacted.
• In every case: clearly identify the sender, inform the person at the time of collection, and offer a simple way to object at any time.

These principles are a summary, not legal advice, and they reflect French and EU rules: other countries differ significantly (for example the United States under the CAN-SPAM Act). Check your own situation, especially if you target several countries. Above all, remember that the right to object is not a constraint against performance: the opt-out link is your best protection against the "Report as spam" button, which is infinitely more costly.

Measure what matters

In outreach, the open rate is a noisy and increasingly unreliable indicator. Focus on four signals, in this order.

• The reply rate: it validates both your targeting and your reputation.
• The bounce rate: above 2%, the list is at fault, stop immediately.
• The complaint rate: the most destructive signal, to watch daily.
• Real placement, measured on addresses with no history with you, and not from your own inbox.

The mistakes that burn a domain

• Prospecting from the company's main domain.
• Sending as soon as the inbox is created, without warm-up.
• Going from 10 to 200 daily sends in a week.
• Ignoring bounces and continuing to send to a dead list.
• Removing the unsubscribe link, thinking it reduces opt-outs.

None of these mistakes can be fixed by better copy. They are corrected upstream, or paid for in reputation. To understand how that reputation is built and measured, see our article on sender reputation, and the mechanism we use on the how it works page.