Rate Limiting

All endpoints are limited to protect the mail2many API from abuse and to ensure fair usage.

Current limits

• 600 requests per minute per API key
• Maximum of 10 concurrent requests per API key

These limits apply per API key and within a time window.

Response headers

You can find the current rate-limit status in response headers:

Header	Description
X-RateLimit-Limit	Maximum number of requests allowed in the current time window
X-RateLimit-Remaining	Remaining number of requests in the current time window

For concurrent requests, the API also provides:

Header	Description
X-ConcurrencyLimit-Limit	Maximum number of concurrent requests per API key
X-ConcurrencyLimit-Remaining	Remaining number of concurrent requests

Behavior when limits are exceeded

When a limit is exceeded, the API returns 429 Too Many Requests.

Example for request-rate limit:

{
  "status": "error",
  "code": 429,
  "message": "Too many requests. Please slow down.",
  "error": "RATE_LIMIT_EXCEEDED",
  "statusCode": 429
}

Example for concurrent-request limit:

{
  "status": "error",
  "code": 429,
  "message": "Too many concurrent requests. Please wait for existing requests to complete.",
  "error": "CONCURRENT_LIMIT_EXCEEDED",
  "statusCode": 429,
  "concurrencyLimit": 10,
  "remaining": 0
}

Additional headers in 429 responses may include:

Header	Description
Retry-After	Seconds to wait before retrying
X-RateLimit-Reset	Time when the current rate-limit window resets (UTC epoch seconds)

Recommended handling

• Wait based on Retry-After or until the time window resets
• Retry the rejected request afterward
• Reduce your request rate permanently
• Reduce concurrent requests (queue/worker limit)
• Use retries with exponential backoff

For general retry strategies, see Fault Tolerance.