Perhaps you're launching a new business, adding a product line under its own brand, or rebranding with a new domain. Updating your web presence is usually near the top of the list. What's easy to overlook is that a new domain also means starting fresh with email.
Gmail, Outlook, and Yahoo have no sending history for your new domain, so they treat it with caution until you prove you're a legitimate sender. Email warmup is how you build that proof. You start with a small number of emails, send them to people who want to hear from you, and gradually increase volume over several weeks. Get it right, and your emails land in inboxes. Rush it, and your emails may land in spam folders for weeks.
Spamhaus notes that for the first 30 days after registration, most spam protection systems place new domains under heightened scrutiny. Reputation damage is hard to reverse: as Spamhaus puts it, "it is much, much easier to drive reputation down than it is to fix a damaged one."
Mailbox providers weigh domain reputation heavily when deciding which emails reach the inbox. IP addresses are tied to your sending infrastructure and can change, but your domain follows you. Get the warmup right and that reputation carries forward.
Set up authentication before your first send
Before sending any warmup email, your domain needs SPF, DKIM, and DMARC records in place. Gmail, Yahoo, and Microsoft all require authentication for bulk senders, and non-compliant messages are rejected before reaching a mailbox.
Our email deliverability guide covers each authentication protocol and the specific requirements for all three providers.
If you're on Sendfully, the domain setup walks you through adding SPF, DKIM, and DMARC records and shows whether each one is verified.
Consider using a subdomain
Before registering a brand new domain for sending email, consider whether a subdomain of a domain you already own (like news.example.com) would work instead. If you're launching a new product line under the same company, for example, a subdomain keeps your sending tied to a domain your customers already recognize.
If you send both marketing and transactional email, use a separate subdomain for each stream. That way, a reputation problem with your newsletters won't affect password reset emails sent from a different subdomain. Each subdomain needs its own warmup, so plan for that when setting up your infrastructure.
Clean your list before you start
If you're warming up with an existing subscriber list, verify your addresses before sending. Hard bounces during warmup are especially damaging to a new domain's reputation. Our guide to email verification APIs covers the major providers and how to choose one.
A practical warmup schedule
Start small and increase volume gradually. Only send to subscribers who opted in, and if you can, try to focus on your most engaged subscribers first. This will help you build reputation faster, which makes the rest of the warmup process easier.
Here's a general schedule:
Days 1-3: Send to 200-500 of your most engaged subscribers, people who have read or clicked an email in the last 30 days. If you don't have engagement data, start smaller (50-100 emails).
Days 4-7: Increase to 500-1,000 per day, still targeting subscribers who have read an email in the last 30 days.
Week 2: Increase volume by 30-50% every few days. Start mixing in subscribers who last engaged 60-90 days ago.
Weeks 3-4: Keep ramping toward your target volume with steady, gradual increases.
To make this concrete: a sender with 50,000 contacts might send to 500 on day one, reach 5,000 per day by the end of week two, and work up to their full list around week five or six.
What to monitor during warmup
Two metrics matter most: bounce rate and spam complaint rate.
Bounce rate: Keep hard bounces near zero. If your overall bounce rate exceeds 2%, something is wrong with your list quality. Remove hard-bounced addresses from your mailing list right away.
Spam complaint rate: Google recommends staying below 0.10% and requires senders stay under 0.30%. Yahoo sets the same 0.30% ceiling. During warmup, when volume is low, even a handful of complaints can push you over these thresholds. This is why sending to engaged subscribers first is helpful.
Our guide to checking your domain reputation covers free tools for tracking your reputation and spam complaint rate during warmup.
Sendfully monitors bounce and complaint rates and automatically pauses sending if our thresholds are exceeded. During warmup, this protects your new domain before reputation issues occur.
Common email warmup mistakes
Sending too much too soon. The most common warmup failure. Sudden volume spikes trigger filtering regardless of how good your content is.
Sending to unverified or purchased lists. High bounce rates and spam trap hits can damage a new domain's reputation fast.
Skipping one-click unsubscribe. Gmail and Yahoo both require one-click unsubscribe for high-volume senders. An unsubscribe is far better for your reputation than a spam complaint. Our guide to List-Unsubscribe headers covers the details.
After warmup
Warmup builds your initial reputation. The good news is that the habits that make warmup work, sending to engaged subscribers, monitoring your metrics, keeping your list clean, are the same habits that keep your emails landing in inboxes long-term. Getting the foundation right makes the ongoing work much easier.