How to warm up a new sending domain

You just set up a new sending domain, configured your SPF, DKIM, and DMARC records, pointed your DNS at your email provider, and now you want to blast 500,000 emails on day one. Do not do that. You will land in spam, get throttled, or get outright blocked.

A new domain and a new IP address have no reputation. To mailbox providers like Gmail, Outlook, and Yahoo, "no reputation" is functionally the same as "bad reputation." They have no evidence that you are a legitimate sender, so they treat you like a suspicious one. That is the problem warming solves.

What warming actually is

Warming is the process of gradually increasing your sending volume over days or weeks so that mailbox providers can observe your sending patterns, engagement metrics, and complaint rates before you hit full volume. You are building a track record. Every batch of email you send during warming is a data point that either builds trust or erodes it.

Think of it like a credit score. A new business with no credit history cannot walk into a bank and get a million-dollar loan. You start small, prove you are reliable, and scale from there. Email reputation works the same way.

Domain warming vs IP warming

There are two reputations in play: the IP address your email is sent from, and the domain in your From header.

IP reputation is the older mechanism. Mailbox providers track the sending history of each IP address. A brand-new IP with no history gets treated with suspicion. If you suddenly pump high volume through it, providers assume something is wrong.

Domain reputation is increasingly the one that matters. Google shifted to domain-based reputation years ago. Microsoft followed. The domain in your From header, your DKIM signing domain, and your return-path domain all contribute. Even if you send from a well-established IP pool, a fresh domain with no reputation will still get filtered.

You need to warm both. If you are on a shared IP pool (more on that below), the IP is already warmed for you. But your domain still needs its own ramp-up period. If you are on a dedicated IP, you are warming both simultaneously.

The warming schedule

There is no universally perfect schedule, but this is a solid baseline that works for most senders. Adjust based on what you see in your metrics.

Period	Daily volume	Notes
Days 1-3	200-500	Your most engaged recipients only
Days 4-7	1,000-2,000	Still prioritize engaged users
Week 2	5,000-10,000	Start broadening your recipient pool
Week 3	20,000-50,000	Monitor closely for deferrals
Week 4+	Full volume	Ramp to your normal sending rate

The exact numbers depend on your total volume and your audience. If your steady-state volume is 10,000 emails per day, you do not need a four-week ramp. Two weeks is probably fine. If you are sending millions, you might need six weeks or longer.

The key principle: gradual, consistent increases. Mailbox providers look for patterns. Erratic volume — 500 one day, 50,000 the next — looks like compromised infrastructure or a spammer testing limits.

Send to your best recipients first

During the first days and weeks of warming, every engagement signal matters disproportionately. Opens, clicks, and replies tell mailbox providers that real humans want your email. Complaints and ignores tell them the opposite.

This means you need to front-load your most engaged recipients. People who opened or clicked your emails in the last 30 days. People who recently signed up. People who actually want to hear from you.

Do not start warming by sending to your full list, which inevitably includes people who have not engaged in months. Those recipients are more likely to ignore your email, mark it as spam, or have abandoned their address entirely. You will tank your reputation before you have one.

If you are migrating from another email provider to Sendkit, segment your list by engagement before you start warming on the new infrastructure. Send to your 30-day actives first, then 60-day, then 90-day, then the rest.

What to monitor during warming

Warming is not a set-it-and-forget-it process. You need to watch your metrics daily and react to what you see.

Bounce rate. Keep it under 2%. If it spikes, stop and clean your list before continuing. Hard bounces during warming are especially damaging because providers are already watching you closely. Our guide on improving deliverability covers bounce handling in depth.

Complaint rate. Google requires this to stay under 0.3%. During warming, aim for well under 0.1%. High complaint rates during the ramp-up period will set your domain reputation back significantly.

Inbox placement. Are your test accounts receiving emails in the inbox or spam folder? Send to seed accounts at Gmail, Outlook, and Yahoo and verify placement after each batch.

Deferrals. These are temporary rejections where the receiving server says "try again later." A few deferrals are normal. A wall of them means the provider is throttling you. Slow down your volume and let things stabilize before increasing again.

Signs warming is going wrong

If you see any of these during your ramp-up, pause and diagnose before continuing.

Bounce rate above 5%. Your list quality is the problem. Validate your addresses before sending more. You are burning reputation on bad data.

Bulk deferrals from Gmail or Outlook. You are ramping too fast for the volume these providers are comfortable accepting from your domain. Cut your daily volume in half and hold steady for a few days.

Spam folder placement across providers. Check your authentication records. Make sure your DKIM is aligned, your SPF includes the sending IP, and your DMARC policy is set correctly. Authentication failures during warming are a death sentence for reputation.

Sudden spike in unsubscribes or complaints. You are sending to people who do not want your email. Tighten your recipient selection. Go back to your most engaged segment and rebuild from there.

Do not try to power through these signals by increasing volume. Warming is about earning trust, and sending more email to providers that are already suspicious of you only makes it worse.

Shared vs dedicated IPs

This is a decision that affects how much warming you actually need to do.

Shared IPs are used by multiple senders on the same platform. On Sendkit, our shared IP pool is already warmed and has established reputation. When you send through our shared pool, you benefit from the collective sending behavior of all senders on that pool. Your domain still needs warming, but the IP side is handled for you. This is the right choice for most senders, especially those doing under 100,000 emails per month.

Dedicated IPs are assigned exclusively to you. Nobody else sends from them, which means nobody else can damage their reputation — but it also means you start from zero. You own the full warming process for both the IP and the domain. Dedicated IPs are available on Sendkit for senders doing 100,000+ emails per month, and they make sense when you need full control over your sending reputation. Check our pricing page for details.

If you are not sure which you need, start with shared. You can always move to a dedicated IP later once your volume justifies it.

Common mistakes that ruin a warm-up

Ramping volume too fast. This is the most common mistake by far. Senders get impatient, skip from 1,000 to 50,000 in a day, and wonder why Gmail is blocking them. Follow the schedule. Be patient.

Sending to cold or unverified lists. If you are warming a new domain and you send to a list you have not mailed in six months, expect high bounces, low engagement, and spam traps. Clean and segment first, send second.

Ignoring bounces during warm-up. Every hard bounce during warming does outsized damage. Process them immediately and suppress those addresses. Do not wait until the warm-up is over to deal with list hygiene.

Changing your sending patterns mid-warm-up. Consistency matters. If you are sending at 10am UTC every day, keep doing that. If you are sending transactional email, maintain a steady flow. Mailbox providers look for predictable patterns during the evaluation period.

Not authenticating properly before starting. If your SPF, DKIM, or DMARC records are misconfigured, warming will not help you. Fix authentication first, verify it is passing, then start your ramp. We have a complete authentication setup guide that walks through every step.

How Sendkit handles warming

If you are sending through Sendkit's Email API or SMTP service, here is what you get out of the box.

Pre-warmed shared IP pool. Our shared sending infrastructure already has established reputation with major mailbox providers. You start with a foundation of trust at the IP level from day one.

Automatic bounce and complaint processing. Hard bounces are suppressed immediately. Complaint feedback loops are processed in real time. You do not have to build this yourself — the platform handles it so your reputation stays clean during warming.

Dedicated IP warming guidance. If you are on a dedicated IP plan, we provide warming schedules tailored to your volume and sending patterns. The docs cover the process in detail, and our team is available to help you through it.

Real-time analytics. Monitor your bounce rate, delivery rate, and engagement metrics as you ramp. You will see problems early enough to course-correct before they become reputation damage.

Warming is not glamorous. It requires patience, clean data, and discipline. But it is the difference between a domain that consistently lands in the inbox and one that fights spam filters forever. Take the time to do it right and you will not have to do it again.