Domain warmup is the process of gradually increasing email send volume from a new sender domain to build trust with mailbox providers like Gmail, Outlook, and Yahoo. A typical warmup runs 4-8 weeks, starting at 5-10 sends per day per mailbox and ramping by 10-20% weekly until reaching steady-state volume of 30-50 sends per day per mailbox. Skipping warmup is the single most common cause of outbound campaigns hitting spam folders within 72 hours of launch.
How does a warmup actually work?
Warmup sends are carefully shaped to mimic the engagement pattern of a healthy inbox. The warmup tool sends low-volume emails to a network of cooperating inboxes that auto-open, reply, and mark as "not spam." Over weeks, this signals to Gmail and Outlook that real humans are engaging with your domain. The mailbox providers track open rate, reply rate, spam-report rate, and the velocity of volume growth; consistent positive signals build sender reputation.
A typical 6-week ramp looks like this. Week 1: 5 sends per day per mailbox. Week 2: 10 sends. Week 3: 20. Week 4: 30. Week 5: 40. Week 6: 50 and considered fully warm. After warmup, the domain can sustain 30-50 sends per day per mailbox indefinitely, as long as engagement holds (real reply rate above 1%, spam reports below 0.1%).
What goes wrong during warmup?
Two things, mostly. First, teams send real cold emails during warmup. Don't. The warmup pool is for warmup only; mixing in cold sends contaminates the engagement signal. Second, teams stop monitoring after warmup completes. Reputation is not permanent. A bad two weeks of low engagement, high bounces, or one spam-report surge will undo months of warmup. The defense is continuous monitoring with placement tests every 7-14 days. ReachIQ Email Health handles warmup and ongoing reputation maintenance across the full sender pool.
Related questions
How long does warmup take?
4-8 weeks for a new domain to reach steady-state outbound volume. Aggressive ramps (2-3 weeks) sometimes work but carry significant blocklist risk. Most professional outbound playbooks treat 6 weeks as the floor for a clean warmup.
Do I need to warm up each new mailbox separately?
Yes. Reputation is tracked at both the domain level and the mailbox level. A new mailbox on an already-warm domain warms faster (2-3 weeks instead of 6), but you cannot skip the ramp entirely. Start every new mailbox at 5-10 sends per day.
What tools handle warmup?
Mailwarm, Warmup Inbox, Mailreach, Lemwarm (from Lemlist), and Instantly all offer warmup pools. Most modern outbound platforms either bundle warmup or integrate with one of these tools. Standalone scripts that simulate warmup without a real engagement pool do not work; mailbox providers detect the pattern.