How to Warm Up a New Email Domain: Step-by-Step Guide for High Deliverability

When customers sign up for AutoSend, the first thing many of them want to do is send. They have a 10,000-person waitlist sitting there, a campaign ready to go, and they just want to hit send.

That instinct will get you blocked.

I have seen it happen more than once. A new domain, zero sending history, 5,000 emails queued up on day one. By day three, deliverability tanks and the founder is wondering why Gmail is dumping everything in spam. The domain reputation is already damaged, and fixing it takes weeks.

Domain warmup is not optional. It is the single most important thing you do before sending at scale.

Why Mailbox Providers Care About Your Sending History

When you send email from a brand new domain, Gmail, Outlook, and Yahoo have no idea who you are. They have never seen traffic from your domain before. Their spam filters treat unknown senders with suspicion by default.

Mailbox providers look at your sending pattern to build a reputation score. A domain that suddenly sends 5,000 emails on day one looks like a spammer. A domain that starts with a small volume, hits good engagement, and scales up slowly looks like a legitimate sender.

Reputation is built from signals: open rates, click rates, spam complaints, and bounce rates. If you send to a cold list with no warmup, you will hit bounces and spam complaints before engagement has a chance to build. That digs a hole that takes months to climb out of.

The rule of thumb: Your domain needs to prove it sends emails people want before you can send at scale.

Before You Start: Technical Foundation

Warmup is not just about volume. You need authentication in place first, otherwise the ramp schedule does not matter.

SPF, DKIM, and DMARC. These records verify that you are authorized to send from your domain. Without them, mailbox providers have no reason to trust you regardless of how gradually you ramp up. The complete guide to email authentication walks through how to set up all three. If you are using AutoSend, here's how to set up your DNS records.

A dedicated subdomain for email. Do not send from your root domain. Use something like mail.yourdomain.com for transactional and campaigns.yourdomain.com for marketing. That way a bad campaign cannot damage your transactional sending reputation.

Postmaster and abuse addresses. Set up [email protected] and [email protected] that actually receive mail. Inbox providers check these.

Webhook endpoints ready. Make sure you can track bounces and complaints in real time before your first send. You need to act on these signals quickly during warmup.

The Warmup Process for Transactional Email

Transactional email is the right place to start. Welcome emails, password resets, order confirmations. These are emails your users asked for. They open them. They click them. That engagement signals to mailbox providers that your domain sends wanted mail. If you are still figuring out what your onboarding email sequence should look like, that is a good place to start since those emails reliably drive early engagement.

If you are sending transactional emails from day one, you are already building reputation passively as your user base grows. Start there before you touch any marketing or campaign sends.

What helps during transactional warmup:

• Keep early emails text-heavy. Plain text or minimal HTML performs better for reputation-building. Spam filters treat image-heavy emails from unknown domains with more suspicion.
• Start with your highest-engagement notifications first. Password resets and order confirmations get opened. Weekly digests and feature announcements can come later once reputation is established.
• Avoid bulk promotional sends during this period. Save campaigns for after you have built transactional credibility.

The Warmup Schedule for Campaign Sends

Transactional emails have a natural warmup built in. Users sign up, emails go out, engagement follows. Campaign sends are different. You are sending to a list all at once, and if the list is large, you need to ramp up deliberately.

Start at 500 emails per day. Multiply by 1.25x each day.

Day	Emails
1	500
2	625
3	781
4	976
5	1,220
7	1,907
10	3,725
14	8,940
21	43,500

At that pace you can reach most list sizes within three to four weeks while giving mailbox providers time to track your engagement between sends. The key is consistency. Send every day, not in bursts. Gaps in the schedule reset the signal.

AutoSend has a gradual send feature built in for exactly this. You set the daily starting volume and the multiplier, and it handles the pacing automatically. Most ESPs do not do this natively, and every customer who skipped manual pacing paid for it with spam folder placements.

Segmentation Strategy During Warming

For campaign sends, do not start with your full list. Segment by engagement level and work through tiers as your reputation builds.

Tier 1 - Highly Engaged: Opened or clicked in the last 30 days, recent subscribers, customers who regularly interact with you. Start here.

Tier 2 - Moderately Engaged: Opened in the last 90 days. Add from week 3 onward.

Tier 3 - Low Engagement: Opened in the last 180 days. Add from week 5 onward.

Tier 4 - Cold/Unengaged: No opens in 180+ days. Consider a reactivation campaign after warmup is complete, not during.

That list of 50,000 contacts you collected over three years? Do not send to them during warmup. Many addresses will be dead, engagement will be low, and the signals will hurt you. Save cold segments for after you have established a foundation.

What to Watch During Warmup

Bounce rate. Keep it under 2%. If you are hitting higher than that, your list has stale addresses. Those stale addresses can also include spam traps, which are even more damaging during warmup than ordinary bounces. Clean your list before continuing.

Spam complaint rate. Google Postmaster Tools will show you this directly for Gmail traffic. Keep it under 0.1%. If it spikes, stop sending and figure out why before continuing.

Open rate. Worth watching as a directional signal, but do not optimize for it. Apple MPP and email proxies inflate open rates artificially. There is more on why open rates mislead and what to measure instead.

Delivery rate. Should stay above 95%. If it drops, you have list quality issues or technical problems.

If bounce rate or complaint rate goes above threshold, pause. Do not push through. The warmup schedule only works when your engagement is clean. You can use a tool like Mail-Tester or GlockApps to test deliverability mid-warmup to see exactly how mailbox providers are scoring you.

Common Mistakes I See

Skipping warmup for a subdomain you think is "clean." A new subdomain has no reputation, even if your root domain is established. It needs its own warmup.

Sending to your full list on day one of using a new ESP. Even if your old domain was warmed up, switching providers can reset your reputation with some mailbox providers because the sending IP changes. Start with your most engaged segment when you switch.

Heavy HTML templates from day one. Images, buttons, tracking pixels, promotional layouts. All of these are fine once your reputation is established. In the first two weeks from a new domain, a plain-text or low-HTML email will land in the inbox more reliably.

Ignoring authentication. SPF, DKIM, and DMARC are prerequisites. If you are not authenticated, warmup does not help you. Google started enforcing DMARC for bulk senders in 2024 and the bar will keep rising. If Gmail is flagging your emails as suspicious, misconfigured authentication is almost always the reason. For a full list of what else can send you to spam, these 18 reasons cover the common ones.

Stopping activity after warmup. Some founders complete warmup and then stop sending for several weeks. Reputation degrades without activity. If you anticipate a gap, keep a minimal volume running to maintain domain freshness.

One Thing to Check Before Your First Send

Most ESPs put new accounts through a verification step before you can send to external addresses. Make sure you have completed that before starting your warmup. If you are still in a sandboxed or restricted state, your warmup sends are not reaching real inboxes.

Once you are sending for real, check whether you are on shared or dedicated IPs. Shared IPs are the default on most ESPs. Your reputation on shared IPs is influenced by other senders on the same pool, which is usually fine early on. Dedicated IPs give you full control but require you to warm up the IP itself alongside your domain. For most early-stage SaaS senders, shared IPs are the right starting point.

After Warmup: Maintaining Your Reputation

Reaching your target volume is not the finish line. Sender reputation requires ongoing maintenance.

Keep sending consistently. Large gaps or dramatic volume changes can hurt your reputation even after a successful warmup. Clean your list regularly. Remove bounces immediately, suppress complaints, and consider removing addresses that have not engaged in 6 to 12 months.

If you want to understand your metrics beyond delivery rate and bounce rate, reading email metrics properly will show you which numbers actually indicate healthy sending.

FAQ

How long does domain warmup take? For most senders starting from zero, a full warmup to high-volume sending takes four to six weeks. If you are starting with a small list under 10,000, you can often complete a usable warmup in two to three weeks.

Do I need to warm up my domain if I am only sending transactional emails? Yes, but transactional email is the easiest warmup path because the emails are triggered by user actions. As long as your bounce rate stays low and you are not sending to dead addresses, transactional sends warm your domain naturally over the first few weeks.

What is the difference between domain warmup and IP warmup? Domain warmup builds sender reputation for your domain name. IP warmup builds reputation for the sending IP address. If you use a shared IP pool (common with most ESPs), IP warmup is handled by the provider. If you use dedicated IPs, you need to warm up both.

Can I speed up domain warmup by sending to my most engaged users first? Yes. Starting with your most engaged segment gives you better engagement signals early. Save the cold or older segments for later in the warmup schedule when your reputation has some foundation.

What happens if I send too much too fast? Mailbox providers will start rate-limiting or blocking your domain. Gmail may start deferring your emails, meaning they eventually deliver but with hours of delay. In serious cases, your domain gets blocklisted and you have to go through a removal process that takes weeks.

Does AutoSend's gradual send feature handle warmup automatically? Gradual send manages the pacing of your campaign sends. You set the starting volume and the daily multiplier, and AutoSend handles the rest. It does not manage transactional email pacing since those fire based on user events, but for campaign sends it removes the manual tracking.

Do I need a separate domain for cold email outreach? Yes, always. Cold email at scale generates spam complaints. Those complaints will damage the reputation of any domain they come from. Use a separate domain for cold outreach and never send marketing or transactional email from it.

What if I switch ESPs after my domain is warmed up? Your domain reputation follows your domain, not your provider. However, plan for a brief re-warming period of one to two weeks when switching, especially if moving to dedicated IPs, since the sending IP changes.