Call rate
The API accepts 500 requests per minute per account. Beyond that it answers 429 Too Many Requests with the X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset and Retry-After headers: wait for the indicated delay before retrying. For high volumes, batch: sending a campaign to a list is a single call, and the CRM API v3 accepts bulk operations on contacts.
API credits
Each account has an API credit quota derived from your email credits: ×5 for subscriptions, identical for pay-as-you-go purchases. API calls, webhooks and OAuth count against it. The api.limit.low and api.limit.reached events warn you before and when the limit is reached (webhook events).
Attachments and request size
- Up to 5 attachments per email, 10 MB per file and 15 MB in total.
- Executable and script files (.exe, .bat, .cmd, .js, .vbs, .msi, .jar, .ps1, .dll…) are refused.
- Attachments travel as base64, which inflates them by about a third in the request.
- For deliverability, stay under 10 MB per email and prefer a download link for large files.
Formats and authentication
- Email API v2 and SMS: JSON or XML, chosen through the URL extension (
.json/.xml). - CRM API v3: JSON, fields in
snake_case(id_sender_email,body_html…). - Authentication: Bearer token (valid 30 days, renewable), API key or OAuth 2.0. All APIs answer over HTTPS only.
Error codes and per-endpoint details: developer portal.