SendGrid 550 temporarily blocked: too many bad requests in a short window

Symptom: 550 saying you are temporarily blocked from sending due to repeated bad requests.

1. Stop sending and wait a few minutes. The block is temporary by design.
2. Find the bad requests: bad from addresses (unverified senders), malformed recipients, or broken payloads in a loop. The block counts bad requests, not volume.
3. Fix the source before resuming. A loop that keeps firing bad requests re-triggers the block immediately.
4. Validate recipients and the from address in your code before calling SendGrid, so malformed input never becomes a bad request.
5. Run the fixed payload through sandbox mode first: a 200 there means the shape is valid and will not count as a bad request.

This is not a rate limit (429) and not a reputation block. It is about request quality, and it is usually your bug.

The official SMTP errors doc: 550 'You are temporarily blocked from sending emails due to repeated bad requests.' Too many bad requests in a short window (bad sender, bad recipient) triggers a block of a few minutes. The general errors doc lists 403 as 'Too many bad requests. Temporary block' on the API side. Sources: http://sendgrid.com/docs/Glossary/emailerrormessages.html | https://docs.sendgrid.com/api-reference/how-to-use-the-sendgrid-v3-api/errors