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.