WTF Series
WTF is Email Warmup?
Gradually building sending reputation on a new IP or domain by starting small and scaling up with real, engaged subscribers.
The real explanation
When you get a new IP address or start sending from a new domain, mailbox providers don't trust you yet. You have no history, no reputation. If you blast 100,000 emails on day one, you'll get throttled, blocked, or sent straight to spam. Warmup is the process of starting with small volumes to your most engaged subscribers and slowly increasing over days or weeks.
A proper warmup plan usually runs 2 to 6 weeks. Day one you might send to 500 of your best openers. Day three, 1,000. By week two, you're at 10,000. By week four, full volume. The key: only send to people who actually open and click during warmup. You're building a track record with mailbox providers. Every open and click is a trust signal. Every spam complaint or bounce during warmup does outsized damage.
Now, about "warmup tools" that use fake engagement: they don't work. Services like Lemwarm or Mailwarm create artificial opens and replies by having accounts interact with your emails. Mailbox providers are wise to this. It inflates your metrics without building real reputation. Real warmup means real subscribers, real engagement, real patience. If you're migrating ESPs, bring your most engaged segment first and earn trust the hard way.
Show me an example
Your company switches ESPs and gets new dedicated IPs. Instead of warming up, the marketing team imports the full 150,000-person list and sends a campaign on day one. Gmail throttles you, Yahoo blocks you, and Outlook sends you to junk. Recovery takes 4 to 6 weeks of careful sending with suppressed segments. If they'd spent those same 4 weeks warming up properly, they'd have been at full volume with clean reputation. Same time, opposite outcome.
Who handles this?
Spark covers warming (new ips/domains).
Go deeper
Read more in the Email Almanac: Email Warmup in the Almanac
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