How to Warm Up a New Sending Domain for B2B Cold Email

A brand-new domain has no sending history, so mailbox providers treat it with suspicion. Send 2,000 cold emails from it on day one and most will land in spam, and the domain may never fully recover. Warm-up is the process of building a positive reputation gradually before you scale.

Step 1: Set up the infrastructure correctly

Before any warm-up, authenticate the domain with SPF, DKIM and DMARC, point it to a simple website or redirect to your main site, and set up two or three inboxes with real names and profile photos. Google's sender guidelines make authentication a baseline requirement for all senders (Google, n.d.). See our SPF, DKIM and DMARC guide.

Step 2: Let the domain age

Domains registered yesterday are a classic spam signal. Register sending domains early, ideally two weeks or more before the first cold message, and use them for warm-up during that time.

Step 3: Ramp volume slowly

There is no official schedule from Google or Microsoft, so treat the following as a conservative practitioner plan per inbox:

To send 600 cold emails a day, you therefore need roughly 15–20 warmed inboxes across five or more domains, not one inbox pushing hundreds of messages.

Step 4: Watch the right signals

• Bounce rate under 2–3%: verify every list first.
• Spam complaints under 0.1% in Google Postmaster Tools (Google, n.d.).
• Placement tests: seed accounts at Gmail, Outlook and Yahoo to see where mail lands.
• Reply rate: a sudden drop to near zero often signals spam-folder placement.

Common warm-up mistakes

1. Sending cold email from your main business domain.
2. Skipping DMARC.
3. Jumping volume after a good week.
4. Using unverified or purchased lists that bounce.
5. Heavy images, attachments or many links in the first emails.
6. Stopping warm-up once campaigns start.

How long until we can launch?

For most clients, a realistic timeline is two to three weeks of warm-up, with the first campaigns going out in weeks three to four. That is slower than "launch tomorrow" promises, but it protects the asset that makes the channel work: your sender reputation. Want us to handle it? See our Launch bundle.