Article

24 November 2025

Viktoria Camp

CEO, CPO, & Co‑Founder of Affinect

Domain warming is the process of slowly increasing how many emails you send from a new or “cold” domain so inbox providers like Gmail and Outlook learn to trust you and put your messages in the inbox instead of spam. Done right, domain warm-up protects your sender reputation, boosts deliverability, and makes your cold outreach or marketing campaigns much more effective.​

In this article
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What is domain warming?

Why does domain warming matter?

How long does a domain warm-up take?

When do you need to warm up a domain?

Step‑by‑step: how to warm up a domain

Best practices for successful domain warm-up

Common mistakes to avoid during domain warm-up

What is the difference between email warm-up and domain warm-up?

How do I know if my domain is warmed up?

Frequently Asked Questions (FAQs)

Domain warming (or domain warm-up) means you start with very low email volume on a new or rarely used domain and gradually ramp it up over days or weeks while keeping engagement high and spam complaints low. Mailbox providers treat new domains as suspicious until they see consistent, wanted, and authenticated traffic, so warming helps you “prove” you are a legitimate sender.​

A “cold” domain is new or has little sending history and therefore low reputation, while a “warm” domain has a history of successful delivery and positive engagement like opens, clicks, and replies. Warming is especially important if you plan to send larger volumes (hundreds or thousands of emails per day) or run ongoing sales and marketing automation.​

• It improves inbox placement, meaning more of your emails land in the main inbox instead of spam or promotions folders.​
• It builds a strong sender reputation with ISPs and spam filters, which protects your brand and keeps you off blocklists.​
• It supports better engagement and ROI from campaigns because emails that actually reach the inbox are far more likely to be opened and clicked.​

Skipping warm-up or sending big volumes too quickly can trigger throttling, greylisting, high bounce rates, or even outright blocking of your messages. Once reputation is damaged, recovery is slow and may require new or secondary domains to start again.​

Most senders should expect warm-up to take anywhere from 2 to 8 weeks, depending on domain age, target daily volume, and how recipients engage with your emails. Smaller goals (for example, around 100 emails per day) usually warm faster than large-scale outreach aiming for thousands of emails daily.​

If engagement is strong and bounce rates stay low, you can sometimes ramp faster, while poor engagement or spam complaints mean you may need to slow down or pause increases. For many sales and marketing teams, a 3–4 week structured warm-up with high‑engagement contacts before heavy cold outreach is a practical baseline.​

You should plan a warm-up phase when:

• You register a brand‑new domain or subdomain for outreach or marketing.​
• You are migrating ESPs, IPs, or sending infrastructure and want to preserve or rebuild reputation.​
• Your existing domain has deliverability problems, blocklisting, or account suspensions, and you decide to introduce a fresh or backup domain.​

It is also smart to warm up separate subdomains if multiple teams are sending campaigns, so you do not overload your main corporate domain. Many brands now maintain a pool of warmed backup domains and mailboxes to avoid downtime if one asset is rate‑limited or blacklisted.​

Here is a simple, practical domain warm-up process that fits both B2B and B2C email outreach:

1. Set up your technical foundations

• Configure SPF, DKIM, and DMARC correctly for your new domain so mailbox providers can authenticate your emails.​
• Use a dedicated subdomain for outreach (for example, “mail.yourbrand.com” or “hello.yourbrand.com”) instead of your primary root domain to reduce risk.​

2. Start with small, highly engaged audiences

• Begin by sending to your most engaged contacts: colleagues, existing customers, or subscribers who recently interacted with your brand.​
• Early warm-up messages should be useful, personal, and likely to get opens and replies, not bulk promotional blasts.​

3. Gradually increase sending volume

• In the first days, many senders start with roughly 10–50 emails per day per inbox and then slowly increase in small steps.​
• Over the next 2–6 weeks, raise volumes consistently (for example, 2× per week) while watching deliverability and engagement metrics closely.​

4. Monitor key metrics every day

• Track inbox vs spam placement, open rates, clicks, replies, bounce rates, and spam complaints.​
• If bounce rates rise above a few percent or spam complaints appear, pause increases, cut volume, clean your list, and fix any content or targeting issues.​

5. Introduce cold outreach or large campaigns

• Once open rates are healthy, spam complaints are minimal, and volume is stable for at least a couple of weeks, you can start mixing in colder lists cautiously.​
• Keep sending patterns stable and avoid sudden spikes in volume, as large jumps can still trigger filters even on a warmed domain.​

• Keep a consistent sending schedule: send regularly on weekdays, not in random bursts.​
• Maintain clean lists: remove invalid addresses and disengaged contacts to keep bounce rates below about 1–3% and protect your reputation.​
• Focus on engagement: use relevant subject lines and content that naturally encourage opens, clicks, and replies instead of spammy wording or all‑caps.​
• Separate warm and cold infrastructure: do not mix very cold domains or shared, risky IPs with warmed assets used for your main campaigns.​

Modern tools can automate parts of warm-up by simulating real conversations, gradually scaling volume, and adjusting based on performance signals. Automation is helpful, but you still need solid data hygiene, good content, and realistic volume goals.​

• Sending too many emails too fast from a new domain.​
• Failing to authenticate with SPF, DKIM, and DMARC before you start sending.​
• Buying or scraping low‑quality lists that lead to high bounce rates and spam complaints.​
• Using misleading or “spammy” subject lines and content that trigger filters.​
• Ignoring engagement metrics and continuing to ramp volume despite poor performance.​

Avoiding these pitfalls keeps your warm-up timeline shorter and reduces the risk of long‑term deliverability damage.​

Email warm-up usually refers to warming up a specific mailbox or sender address, while domain warm-up focuses on the overall sending reputation tied to your domain or subdomain. In practice, both involve gradually increasing volume and engagement, but domain warm-up has a broader impact across all mailboxes using that domain.​

Some tools offer mailbox‑level warm-up (for example, simulating replies from other real inboxes), which supports but does not replace domain‑level reputation building. For reliable deliverability, you generally want both: a well‑warmed domain and properly warmed key sending inboxes.​

You can consider a domain “warmed” when:

• Your emails consistently land in inboxes (not spam) across major providers like Gmail and Outlook.​
• Engagement is stable at acceptable levels with low bounce rates and minimal spam complaints over multiple weeks.​

Brands often validate this by monitoring placement across test inboxes, checking reputation dashboards, and watching metrics as they introduce higher volumes or colder audiences. If performance drops, treat it as a signal to slow down and tighten your sending and list practices.​