Reference
Rate limits, quotas, and usage
How much you can send, how fast, and how to check where you stand.
Rate limits
Each API key can make 10 requests a second. Responses to authenticated requests carry these headers:
| Header | Meaning |
|---|---|
ratelimit-limit | Requests allowed per window. |
ratelimit-remaining | Requests left in the current window. |
ratelimit-reset | Seconds until the window resets. |
retry-after | On a 429, seconds to wait before retrying. |
Past the limit, requests fail with 429 rate_limit_exceeded. Wait for retry-after and try again, or use batch sends to send more per request.
Monthly sends
Each plan includes a monthly allowance, shared by mailbox mail, SMTP relay, and the API. Every email counts once, however many recipients it has. Past the allowance, sending continues and extra sends are billed per 1,000, up to a cap of twice the allowance by default:
| Plan | Included sends | Sending stops at |
|---|---|---|
| Mini | 15K | 30K |
| Business | 75K | 150K |
| Enterprise | 250K | 500K |
At the cap, sends fail with 429 monthly_quota_exceeded until the next billing period. If a payment is overdue, sending is held to the included allowance. See pricing for per-1,000 rates.
Size limits
| Limit | Value |
|---|---|
Recipients per email (to + cc + bcc) | 50 |
| Attachments per email, total | 40 MB |
| Emails per batch | 100 |
| Batch request body | 20 MB |
| Scheduling window | 30 days |
| Idempotency key lifetime | 24 hours |
Paused sending
To protect deliverability for everyone, Chebu watches bounce and complaint rates over the last 7 days once a workspace has sent at least 200 emails. At a 10% bounce rate or a 0.5% complaint rate, sending pauses until our team reviews it, and requests fail with 403 workspace_paused. Keeping lists clean and honoring the suppression list keeps you well below that.
Check usage
/usagecurl https://api.chebu.io/usage \
-H "Authorization: Bearer $CHEBU_API_KEY"{
"period_start": "2026-09-01T00:00:00Z",
"period_end": "2026-10-01T00:00:00Z",
"plan": "business",
"sends": { "used": 18240, "included": 75000, "cap": 150000 },
"storage": {
"used_bytes": 21474836480,
"included_bytes": 107374182400
},
"domains": { "used": 2, "included": 3, "extra": 0 },
"mailboxes": { "used": 14, "included": 30, "extra": 0 }
}