How many inboxes per domain for cold email?

Use two to three inboxes per sending domain, and send around 30 to 50 cold emails a day from each warmed inbox. That gives a domain a safe capacity of roughly 60 to 150 emails a day. To work out how many domains you need, divide your daily send target by inboxes per domain times emails per inbox. Never send cold email from your main company domain.

TL;DR

• Inboxes per domain: two to three. More concentrates risk on one domain.

• Emails per warmed inbox: about 30 to 50 a day; start new inboxes at 5 to 10.

• Domains needed = daily target ÷ (inboxes per domain × emails per inbox).

• Warm up new domains and inboxes for two to four weeks before cold sending.

The short answer

Most experienced senders land on two to three mailboxes per domain as the practical middle (FirstSales). After warm-up, a common steady-state target is 40 to 50 emails a day per inbox, with two to three inboxes per domain (Prospeo). Many teams run lower, around 20 to 30, to stay well inside limits.

Why not more inboxes per domain?

Reputation sits with the domain as well as the inbox. Ten inboxes on one domain means one bad campaign can damage all of them at once. Spreading inboxes across domains limits the damage.

Mailbox providers have also tightened. Google requires bulk senders (5,000+ messages a day to Gmail) to authenticate their email, offer one-click unsubscribe and keep spam rates low (Google). Cold email at volume needs to look and behave like normal business email.

How many domains you need

The formula: domains needed = daily send target ÷ (inboxes per domain × emails per inbox) (FirstSales).

At three inboxes per domain and about 35 emails per inbox:

• 100 emails a day: about 3 inboxes on 1 domain.

• 300 a day: about 9 inboxes on 3 domains.

• 500 a day: about 15 inboxes on 5 domains.

• 1,000 a day: about 29 inboxes on 10 domains.

Add a buffer of around 20% for inboxes resting or recovering.

Warm-up and ramp

1. Register domains and let them age before sending.

2. Set up SPF, DKIM and DMARC. See our SPF, DKIM and DMARC guide.

3. Warm up for two to four weeks, starting at 5 to 10 emails a day.

4. Ramp gradually to your steady-state volume.

5. Monitor bounce, spam and reply rates weekly, and rest inboxes that slip.

Do you even need that much volume?

More inboxes aren't the goal. A small setup sending relevant emails to a well-chosen list usually beats a large one sending generic emails. Start with the volume your list and offer can justify.

For infrastructure, see cold email inbox providers, email warm-up tools, cold email deliverability and cold email benchmarks. Our outbound team sets up and runs this infrastructure for clients.

FAQ

How many inboxes should I have per domain for cold email?

Two to three. More concentrates risk on a single domain.

How many cold emails can I send per inbox per day?

Around 30 to 50 from a fully warmed inbox, with many teams staying at 20 to 30. Start new inboxes at 5 to 10 a day.

How many domains do I need for 500 cold emails a day?

About five domains with three inboxes each, sending around 35 emails per inbox.

Can I send cold email from my main domain?

No. Use separate sending domains so a problem never affects your company's everyday email.

How long should I warm up a new inbox?

Two to four weeks before full cold sending, ramping gradually from 5 to 10 emails a day.

About this guide

We are GROU, a B2B pipeline agency that runs lead generation, outbound, and LinkedIn content for clients across manufacturing, fintech, iGaming, software, and professional services. Guidance draws on Google's sender requirements and the sources linked inline, checked September 2026.

These are working ranges, not guarantees. Watch your own bounce, spam and reply data and adjust.