No inbox provider publishes a safe number for cold email. Google, Yahoo and Microsoft publish rules for authentication, complaints and unsubscribing,12 not a daily quota for prospecting. The numbers below are the playbook’s defaults: deliberately conservative, because a burned domain costs a month to replace and a slower ramp costs a few days.
What’s the daily limit per mailbox?
| Setting | Default |
|---|---|
| First cold email | After 3–4 weeks of warm-up, on a domain at least 30 days old |
| Starting volume | 10 cold emails a day per mailbox |
| Daily increase | 1–2 emails a day, no jumps |
| Steady state | 15–25 a day per mailbox |
| Ceiling | Never above 30 |
| Mailboxes per domain | 2–3 |
| Spare warmed mailboxes | About 10% of the fleet |
What does the ramp look like week by week?
| Week | Warm-up a day | Cold a day | Goal |
|---|---|---|---|
| 1–3 | 5, rising to 20 | 0 | DNS passing, profile set, test emails land in the inbox |
| 4 | About 15 | 10 | First small campaign to your best segment |
| 5 | About 10–15 | 15–20 | Bounces under 1%, no angry replies |
| 6+ | About 10 | 20–25 | Steady state; grow sideways from here |
Whether to keep warm-up running after launch is genuinely debated; the warm-up guide covers both sides.
How many mailboxes and domains do I need?
Work backwards from the meetings you want. The calculator does this for you, but the arithmetic is short:
- Emails a working day = meetings a month × emails per meeting ÷ about 21 working days.
- Mailboxes = emails a day ÷ your per-mailbox volume, plus 10% spares, rounded up.
- Domains = mailboxes ÷ 2–3, rounded up, and never fewer than three.
Example: 8 meetings a month at 200 emails per meeting is about 76 emails a working day. At 20 per mailbox that’s 5 mailboxes with spares. The arithmetic says two domains; use three, so losing one never stops you.
A starting setup of 3–5 domains with 2–3 mailboxes each gives 6–15 mailboxes, enough for roughly 100–300 cold emails a day once warm.
Is the limit different for Google Workspace and Microsoft 365?
The defaults are the same, but the failure modes differ. Google is strict on brand-new accounts that send volume fast, and in late 2025 it suspended many cold-email mailboxes, hitting free, discounted and shared accounts hardest.3 Microsoft tends to suspend less often but applies tenant-level limits, so a few bad mailboxes can restrict a whole organisation’s sending.4 Keep Microsoft tenants small. More in Google Workspace vs Microsoft 365.
What happens if I send too much?
Watch for these signs before they become a burned domain:
- Temporary rate limits. Gmail answers with
421 4.7.28, “Gmail has detected an unusual rate of email” or “…of unsolicited email” from your domain or IP.5 Slow down now and check your targeting. - Outright blocks.
550 5.7.1means the message looks unsolicited or your reputation is very low.5 Pause and work through the spam checks. - Quiet mailboxes. One mailbox stops getting replies while others with the same copy and list hold steady. It’s usually landing in spam.
Why spread volume instead of sending more per mailbox?
Reputation lives in three places: the sending IP, the domain and the mailbox. With Google Workspace or Microsoft 365 the provider owns the IP, so your risk sits in domains and mailboxes. Losing one mailbox is a small loss; losing a domain takes every mailbox on it. Many small, properly warmed mailboxes across several domains mean one bad week never stops the whole programme.
Common questions
How many cold emails can I send per day from one Gmail or Google Workspace account?
The playbook’s default is to start at 10 cold emails a day once the mailbox has had 3–4 weeks of warm-up, rise by 1–2 a day to 15–25, and never go above 30. Google doesn’t publish a safe cold-sending volume, so treat this as a conservative default, not a rule.
How many mailboxes should I have per domain?
Two or three. Spread mailboxes across at least three sending domains and keep about 10% of them warmed and idle as spares, so losing one domain never stops you.
How do I send more cold email safely?
Add mailboxes and domains, never more volume per mailbox. If you need 500 emails a day at 20 per mailbox, that’s 28 mailboxes with spares across about 10 domains, not 5 mailboxes at 100 a day.
Keep reading
Sources
- Google: Email sender guidelines. support.google.com
- Microsoft: Outlook requirements for high-volume senders, 2025. techcommunity.microsoft.com
- Salesforge: Google’s cold-email mailbox suspensions, October 2025 (vendor estimate). salesforge.beehiiv.com
- EmailBison: Google Workspace vs Microsoft 365 for cold email (vendor data). emailbison.com
- Google: Gmail SMTP errors and codes. knowledge.workspace.google.com