too_many_recipients

Status: 422 · Code: too_many_recipients

A single POST /v1/emails can have at most 50 addresses across to + cc + bcc combined. This is a deliverability guardrail, not a billing one.

How to fix

Pick the shape that fits:

• One message, many recipients (each sees their own to): loop over the list and call POST /v1/emails once per recipient. Use idempotency_key so retries don't duplicate.
• One shared message (e.g. a newsletter): break the list into batches of 50 and submit each. The API doesn't auto-batch — that's deliberate so you stay in control of retry and throttle behaviour.
• Large marketing send (> 1000 recipients): this sizing usually means you want a campaign, not a raw send. Campaign APIs are on the roadmap — until then, batch at your end and throttle to your workspace's rate_limit_per_minute.

Related

• Idempotency
• Rate limits