Email Warmup
Also called: Inbox Warmup, Domain Warmup, Email Warming
Definition
The process of gradually increasing sending volume on a new email domain or inbox to build a positive sender reputation before launching cold email campaigns.
Email warmup is the mandatory first step before any cold email campaign. A brand-new domain or email address has no sending history — major email providers (Gmail, Outlook, Yahoo) don’t know whether it’s a legitimate sender or a spammer. Starting a campaign immediately on a new domain results in poor inbox placement, high spam rates, and potentially permanent domain blacklisting.
How warmup works
The goal is to build a history of positive engagement on the domain: emails sent, emails opened, emails replied to. Warmup tools automate this by sending emails between a network of real email accounts and generating the engagement patterns that indicate legitimate sender behaviour.
Typical warmup schedule:
- Week 1: 5–10 emails/day
- Week 2: 15–25 emails/day
- Week 3: 30–50 emails/day
- Week 4+: 50–100 emails/day
- Campaign launch: 6–8 weeks after domain creation
Warmup tools
- Mailreach: Dedicated warmup network with reputation monitoring
- Warmup Inbox: Network of real accounts for engagement-based warmup
- Instantly.ai: Includes warmup as a feature alongside sequencing
- Lemlist: Warmup network included with sequencing subscription
What happens without warmup
Without warming, a new domain sending 200 cold emails on day 1 will be flagged as a spam source within days. The domain’s reputation tanks, inbox placement drops below 10%, and the domain may be blacklisted permanently — meaning it’s useless for future outreach.
Related concepts
Email warmup is the operational step between domain setup (SPF/DKIM/DMARC configuration) and campaign launch. Domain reputation is the output being built during warmup.
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