The Email Warm-Up Plan: How to Build Sender Reputation From Scratch

You've set up your dedicated sending domain. SPF, DKIM, and DMARC are passing. Your Klaviyo account is connected to Shopify, flows are built, and you're ready to start sending. There's one problem: Gmail has never seen an email from this domain before.

New sending domains have no reputation. Not bad reputation — no reputation. And inbox providers treat unknown senders with suspicion. If you send 50,000 emails from a brand-new domain on day one, Gmail will throttle delivery aggressively. Emails will land in spam, get deferred, or bounce. The engagement metrics from that first send will be terrible, and those terrible metrics become your domain's first impression.

The warm-up process exists to build reputation gradually. You start small, send to your most engaged subscribers (who are most likely to open and click), generate positive engagement signals, and expand volume over time. Gmail watches this pattern and progressively trusts your domain with larger sends.

Here's the warm-up schedule we use for new Klaviyo accounts. The exact numbers scale based on total list size, but the principles are consistent.

Week 1 is about proving legitimacy. Send to your Engaged 14-day segment only — subscribers who opened or clicked an email in the last two weeks. These are your most active subscribers and the most likely to engage. Send 1-2 campaigns this week. Keep the content strong: a compelling subject line, clean design, clear CTA. Every open and click in this first week is building the foundation.

If your list is entirely new (no engagement history), start with your most recent subscribers — people who signed up in the last 30 days. Recency is a decent proxy for engagement when you don't have open/click data yet.

Week 2 expands to Engaged 30-day subscribers. This roughly doubles your audience while still targeting people with demonstrated recent interest. Send 2-3 campaigns. Continue monitoring bounce rates (should be under 2%), spam complaints (under 0.05%), and open rates. If open rates are above 30%, you're on track.

Week 3 adds the Engaged 60-day segment. You're now reaching the majority of your active list. Send 2-3 campaigns. This is where you'll start seeing a more realistic picture of your engagement metrics. Some Gmail-heavy lists will show slight dips in open rates at this stage — that's normal as you reach less-engaged subscribers.

Week 4 reaches your Engaged 90-day segment, which should be your maximum campaign audience going forward. By this point, you've established 3-4 weeks of positive sending history. Gmail has data showing your domain sends emails that people open and click. Your reputation is established enough to handle full-volume sends.

What you should never do during warm-up: send to your full list including unengaged subscribers, send more than one campaign per day, send to purchased or imported lists that haven't been verified, dramatically increase volume overnight (keep increases at 2x or less per week), or ignore bounces and complaints hoping they'll resolve.

Flows behave differently during warm-up. Automated flows like Welcome Series and Abandoned Checkout will fire as soon as they're live, regardless of your campaign warm-up schedule. This is actually helpful — these flows go to people who just took a high-intent action (signing up, abandoning checkout), so engagement rates tend to be strong. The flow volume supplements your campaign warm-up by adding more positive engagement signals.

Monitoring during warm-up requires checking three things daily. Bounce rate: if hard bounces exceed 2% on any send, pause and clean your list before the next send. Spam complaints: if any send generates more than 0.08% complaints, the content or targeting needs attention. Open rate: watch for sudden drops that suggest Gmail is filtering emails to spam.

Google Postmaster Tools is essential during warm-up. Sign up, verify your domain, and monitor your domain reputation directly from Google's perspective. It'll show you whether Gmail classifies your domain as High, Medium, Low, or Bad reputation. During a healthy warm-up, you should see reputation climb from unknown to Medium or High within 2-3 weeks.

For brands migrating from another ESP (like Mailchimp to Klaviyo), the warm-up is still necessary even though your subscribers already know you. The new sending infrastructure has different IP addresses and different authentication, so Gmail treats it as a new sender. The warm-up can sometimes be compressed to 2 weeks instead of 4, but skipping it entirely risks deliverability problems.

The warm-up is the least exciting part of building an email program. There's no revenue milestone to celebrate after week one. But it's the 30 days that determine whether the next 12 months of email marketing reach inboxes or spam folders. Every brand we've taken from $0 to meaningful Klaviyo revenue started with a disciplined warm-up that built the reputation foundation everything else depends on.