How to warm up a new email domain

Mailbox providers decide where your mail goes from what they observe. Microsoft's Dynamics 365 warm-up documentation lists the inputs: spam complaints, hard bounces from invalid addresses, spam trap hits, authentication through SPF, DKIM and DMARC, third-party blocklisting, and engagement. Opens, clicks and passing authentication help. Weak permission, complaints, bad addresses, blocklistings, trap hits and large spikes in volume hurt.

Domain and IP reputation are tracked separately. Mailgun's guide to domain warm-up explains that a shared IP from a sending provider is already warm. A new dedicated IP starts blank. Mailgun also notes that providers look at a domain's history across the internet, its sector, and how long it has been registered. That is why a domain bought last week starts behind one that has existed for years, even when both have sent nothing.

Reputation also does not move with you. Microsoft states plainly that you cannot transfer reputation from one domain to another. A new domain starts from zero no matter how well your old one performed.

Warm-up does nothing for a domain that fails authentication. Finish these steps before you send a single message:

1. Publish SPF so receivers can confirm which servers are allowed to send for the domain.
2. Sign with DKIM on your own domain. Postmark's domain warm-up guide recommends signing with your own domain rather than your provider's, because that builds your domain's reputation faster.
3. Use a custom Return-Path that matches your domain. Postmark notes that receivers use the Return-Path domain for SPF, so aligning it with your domain also speeds up reputation building.
4. Add a DMARC policy to your From domain. Together with custom DKIM and Return-Path, Postmark says this protects the reputation you are about to build.
5. Check every link in your template. Postmark counts link domains as a fourth reputation in play, including tracking links, short URLs and file hosting. In its experience, links hurt delivery mainly when they look deceptive or malicious.

Then decide which mail goes on which domain. Postmark describes subdomains as developing their own reputations, like branches of a tree. The parent domain still sets the ceiling, but each branch grows on its own. Put transactional mail and promotional mail on separate subdomains, so a bad bulk send cannot drag down password resets and receipts. For cold outreach the same reasoning argues for a separate domain entirely. If outreach goes badly, it should not take the domain your customers and colleagues rely on down with it.

Postmark and Microsoft both publish concrete figures. They do not agree on every number, which shows how much depends on your list and your receivers. Treat these as ranges to steer by, not rules.

This is the case Postmark and Microsoft write for. You have a list of real subscribers or customers, and you are moving their mail onto a new domain.

Split your list by receiver.Postmark's first step is knowing how much of your mail goes to Gmail, Yahoo, AOL, Microsoft and other providers. Each receiver has its own threshold for a new domain, so you ramp each one separately.

Weeks 1 and 2: only your most engaged recipients.Send to people who opened or clicked in the last 30 days, which is Microsoft's window. Start at the low end of Postmark's schedule, 50 to 100 per provider on the first two days. Double only when opens and bounces look healthy. Keep the content simple and useful.

Weeks 3 and 4: widen carefully.Add people who engaged in the last 60 days. Once daily volume is substantial, slow the ramp to Postmark's 20% to 50% per day. Add older segments in chunks no larger than 15% of your current volume, as Microsoft advises, so one weak segment cannot tip your reputation.

Weeks 5 and beyond: reach full volume. Keep anyone who has been silent for 90 days out of the first six weeks entirely. Stay consistent on volume and frequency. Microsoft notes that sending less often than weekly makes reputation take longer to build.

Before every increase, look at each receiver. Postmark's rule is to never raise volume until you have checked performance receiver by receiver. If engagement and bounces look normal, go up the next day. If they slip, drop 25% to 30% and hold there until they recover.

Outreach changes the problem. You are not migrating an engaged list. You are writing to strangers who have never opened your mail. You may also be sending from a few Google Workspace or Microsoft 365 mailboxes rather than a sending service. Microsoft points out that B2B senders face the same filters as everyone else, because many business domains are now hosted by Gmail, Outlook, Yahoo and AOL.

With no engaged list to start from, a new mailbox has to build its history some other way:

• Manually. Send real mail to colleagues, partners and existing contacts who will reply. This works, but it is slow, and it gets impractical across several domains with several mailboxes each.
• Automatically. A warm-up tool connects the mailbox to a network of other mailboxes. They exchange messages, open them and reply on a schedule that rises gradually. Our guide to how long to warm a mailbox covers the timing in more detail.

Be clear-eyed about what automated warm-up proves. Mailgun criticizes paid services that use fake accounts to make a mailbox look trusted. It calls that approach unethical, and says it backfires when real recipients mark the mail as spam. Warm-up activity is also a closed loop: the mailboxes in a network open and answer each other, so near-perfect delivery inside it says little about how a cold email to a stranger will land. Two habits fix that:

1. Test real content before you scale. Send a small batch of your actual outreach email to a seed or inbox placement test, and check where it lands at each provider.
2. Treat the warm-up score as a floor, not a green light. Our look at whether email warmup works goes into what warm-up can and cannot do for you.

Provider-specific setup differs too. The Google Workspace warming page and the Microsoft 365 warming page cover each one.

Some trouble early on is normal. Microsoft tells senders to expect some bulking, meaning mail filed as spam, and some blocking in the first weeks. The advice is to stick with the plan.

• Spam-folder placement at Gmail, Yahoo or AOL. Microsoft says this usually clears after a few sends with solid engagement. Keep sending to your most engaged recipients.
• Delays at AOL, Microsoft or Comcast. Temporary 421 responses retry for 72 hours before turning into a hard bounce. They are not a concern as long as the mail eventually delivers. If many messages time out, shrink volume to that provider by tightening your engagement window.
• Blocks. These usually mean the list is not engaged enough. Segment more tightly and keep sending to the people most likely to open.
• Rising bounces or falling opens at one receiver. Cut that receiver's volume by 25% to 30%, following Postmark's rule, and hold it there until the numbers recover.

Mailgun describes the cost of skipping warm-up: throttling, greylisting and outright blocking. Those same three signals tell you a ramp is moving too fast.

How long does it take to warm up a new domain?

Postmark puts it at 3 to 6 weeks for most senders. Microsoft says 4 to 8 weeks to maximum deliverability. Both say it takes longer when recipients do not clearly want the mail. Reputation needs time to build at each volume level, so a clean two weeks is not the finish line.

Can I start sending real campaigns after two weeks?

Two weeks with clean delivery is a good sign, but both guides' timelines run well past it. Start real sends small, test placement with your actual content, and keep ramping.

Should I stop warm-up once campaigns start?

For outreach mailboxes, keep warm-up running alongside real sends. Reputation is scored continuously. A mailbox that stops generating positive signals while it sends low-reply cold mail can lose ground. Turning warm-up off once a score hits its maximum is how people end up starting over.

Do warm-up emails count toward a mailbox's daily volume?

Yes. Providers see everything the mailbox sends, not just your campaigns, so plan warm-up and real sends as one daily total.

My main domain already lands in spam. Should I switch domains?

A new domain starts with no reputation, because reputation does not transfer between domains, so switching only trades a bad record for an empty one. Move cold outreach to a separate domain and warm it properly. Then let your main domain recover by sending it only mail people want.

I use a shared IP from my email provider. Do I still need to warm up?

Yes. Mailgun notes that a shared IP is already warm, but your domain is still new. Microsoft adds that providers like Gmail weigh domain reputation together with IP reputation, so the domain warm-up still applies.

If you are warming several outreach mailboxes on a new domain, doing it by hand gets slow quickly. SuperWarm automates warm-up for Google Workspace and Microsoft 365 mailboxes. You connect each mailbox with OAuth, and SuperWarm keeps it warming in the background. It does not send campaigns: you keep sending from those mailboxes with whatever outreach tool you already use.

Ten mailboxes are free, and unlimited mailboxes cost $49 a month. If you are still comparing options, the roundup of email warmup tools lays them side by side. Otherwise, you can create your free account and connect your first mailbox.