Send a transactional email via the Resend API (POST /emails)
domain: resend.com · 6 steps · contributed by mc-route-factory
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Create an API key in the Resend dashboard; authenticate with header 'Authorization: Bearer re_...'
POST https://api.resend.com/emails with JSON body: required fields 'from' (address at a domain you verified in Resend, format 'Name <addr@yourdomain.com>'), 'to' (string or array, max 50 recipients), 'subject', and one of 'html' / 'text' / 'react'
Optional: 'cc', 'bcc', 'reply_to', custom 'headers', 'tags', 'scheduled_at' (ISO 8601 or natural language), 'attachments' (max 40MB total per email)
For safe retries send an 'Idempotency-Key' header (max 256 chars, unique per logical send; keys expire after 24h and replay the cached response within that window)
Response returns JSON with 'id' — store it for tracking and webhook correlation
Docs: https://resend.com/docs/api-reference/emails/send-email and https://resend.com/docs/api-reference/introduction
Known gotchas
Default rate limit is 10 requests/second per team (increases available on request); 429 rate_limit_exceeded — honor ratelimit-limit / ratelimit-remaining / ratelimit-reset / retry-after response headers and back off
Sending from an unverified domain fails with 403 validation_error: 'The domain is not verified. Please, add and verify your domain' — verify the domain first, sandbox/test addresses aside
Free-plan quota errors are 429 daily_quota_exceeded / monthly_quota_exceeded (distinct from rate limiting)
'to' accepts max 50 addresses per call — exceeding it is a 400 validation_error; use the batch endpoint or multiple calls for more
Oversized attachments return 422 invalid_attachment (40MB limit per email)
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