Email Warmup

Email Warmup

Gradually ramp sending volume on new domains and IPs so mailbox providers trust you before you need to send at scale.

When to use this skill

• Setting up a new sending domain or subdomain
• Switching to a dedicated IP address
• Moving to a new email service provider (even with an existing domain)
• Resuming sending after a long period of inactivity (30+ days)
• Scaling up from low volume to high volume sending
• Seeing deferrals, throttling, or spam folder placement on a new domain
• An AI agent needs to send email and you haven't established sending history yet

Related skills

• domain-authentication - SPF, DKIM, and DMARC must be in place before you start warming up
• sender-reputation - warmup builds initial reputation; this skill covers maintaining and recovering it
• rate-limiting - volume controls that protect reputation during and after warmup
• inbox-placement - factors beyond warmup that determine inbox vs spam
• bounce-handling - processing delivery failures during warmup without compounding damage

Why warmup matters

Mailbox providers (Gmail, Microsoft, Yahoo) track sending behavior per domain and per IP. A domain or IP with no sending history is unknown - not trusted, not distrusted. When an unknown sender suddenly pushes thousands of messages, it looks indistinguishable from a spammer who just registered a fresh domain.

Warmup is the process of sending gradually increasing volumes of email to build a positive reputation before you need full throughput. Skip it and you'll hit deferrals, spam folder placement, or outright blocks that can take weeks to recover from.

Domain warming vs IP warming

In 2025, domain reputation is more important than IP reputation for most senders. Here's why:

Domain reputation follows you everywhere. When you switch providers (Postmark to SendGrid, SES to Resend), your domain reputation comes with you. IP reputation resets. Gmail and Microsoft shifted their filtering algorithms toward domain-centric signals starting in 2024, because domain reputation is harder to game - you can't just rotate to a new domain the way spammers rotate IPs.

IP reputation still matters, but less often. If you're on a shared IP pool (which most senders under 50,000 emails/month are), IP warming isn't your problem - the provider manages it. You only need to worry about IP warming when you move to a dedicated IP, which is typically only worth doing above 50,000-100,000 emails per month.

Every new combination needs warming. A warm domain on a new IP still needs IP warming. A warm IP with a new domain still needs domain warming. Changing both at once (new provider + new domain) is the hardest scenario.