Limits

Limit	Value
Requests per API key	10 per second on POST /emails and POST /emails/batch
Recipients per email	50 (to + cc + bcc)
Emails per batch	100
Attachments	30 MB in total per email
Tags	10 per email
Subject	998 characters
Scheduling	Up to 30 days ahead
Idempotency keys	Remembered for 24 hours

Daily limit

Each team has a daily sending limit, counted per recipient and reset at midnight IST. New accounts start at 100 per day; the limit rises as you build a clean sending history. Test-mode addresses don’t count. Over the limit, requests return 429 daily_quota_exceeded.

Rate limit headers

Sending responses tell you where you stand:

RateLimit-Limit: 10
RateLimit-Remaining: 7
RateLimit-Reset: 1

Over the limit you get 429 rate_limited with a Retry-After header in seconds. Wait that long, then retry. With an idempotency key retries are always safe.