Deliverability isn't luck, and it isn't a "spam word" checklist. It's infrastructure. If your cold emails are landing in Promotions or Spam, the fix almost never lives in the copy. It lives in how your domains, mailboxes, and sending behavior were set up in the first three weeks.

We run cold outbound for B2B SaaS teams every day, and the single most common reason a campaign underperforms is that someone tried to send volume from a domain that wasn't ready. Here's the sequence we actually use, and the mistakes that quietly torch a domain before a single reply comes back.

First, understand what the inbox is scoring

Mailbox providers like Google and Microsoft don't read your email and decide it's spam. They score reputation for your domain, your IP, and increasingly your specific sending patterns, then route accordingly. Three signals dominate:

  • Authentication: can the provider cryptographically confirm you are who you say you are?
  • Engagement: do real people open, reply, and not mark you as spam?
  • Consistency: does your sending volume ramp like a human, or spike like a bot?

Everything below is about winning those three, in order.

Week 0: never send from your primary domain

This is the decision that protects your brand forever. We register dedicated sending domains, lookalikes of your primary such as get-yourbrand.com, and send cold volume only from those. If a sending domain ever gets burned, your real domain, and the email your customers and investors reach you on, is completely insulated.

The goal of warmup isn't to trick the inbox. It's to build a track record that happens to be true.

Set authentication up correctly, once

Before any warmup, every sending domain gets the full trio configured and verified:

  • SPF authorizes your sending servers.
  • DKIM signs every message.
  • DMARC tells providers what to do when the first two don't line up, and gives you reporting.

Skipping DMARC is the most common setup miss we see. It stopped being optional. Google and Yahoo now require it for bulk senders, and skipping it is a fast track to the spam folder.

Weeks 1–3: warm up like a human, not a firehose

A brand-new mailbox that suddenly sends 200 cold emails on day one looks exactly like a compromised account. Warmup earns trust by starting tiny and ramping predictably:

  1. Days 1–5: a handful of sends per mailbox per day, mostly to seed inboxes that open and reply.
  2. Days 6–14: gradually increase volume while keeping reply rates high and complaints at zero.
  3. Days 15–21: layer in real campaign sends, still capped well below the mailbox's ceiling.

Throughout, we keep per-mailbox volume conservative and spread sends across many mailboxes rather than blasting from a few. Slow is fast here: three patient weeks buys you months of primary-inbox placement.

The mistakes that torch a domain

Even with good infrastructure, a few habits will undo it:

  • Buying a cheap, unverified list and mailing it. Bounces and spam traps wreck reputation instantly.
  • Sending identical, un-personalized copy at volume.
  • Ignoring your bounce rate. Above ~3% and providers start throttling you.
  • No working unsubscribe. It's a compliance requirement and a reputation signal.

How to know it's working

You don't have to guess. Seed-inbox tests across Gmail, Outlook, and Yahoo tell you exactly where you're landing, and DMARC reports confirm authentication is holding. When placement is right, the reply rate takes care of itself. That was always the only metric that mattered.

Get the first three weeks right and deliverability stops being something you think about. That's the whole point.