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

TL;DR

Run the fixed payload through sandbox mode first: a 200 there means the shape is valid and will not count as a bad request. Fix the source before resuming.

Steps

1. Symptom: 550 saying you are temporarily blocked from sending due to repeated bad requests.
2. Stop sending and wait a few minutes. The block is temporary by design.
3. Find the bad requests: bad from addresses (unverified senders), malformed recipients, or broken payloads in a loop. The block counts bad requests, not volume.
4. Fix the source before resuming. A loop that keeps firing bad requests re-triggers the block immediately.
5. Validate recipients and the from address in your code before calling SendGrid, so malformed input never becomes a bad request.
6. Run the fixed payload through sandbox mode first: a 200 there means the shape is valid and will not count as a bad request.
7. This is not a rate limit (429) and not a reputation block. It is about request quality, and it is usually your bug.

When to use

You are seeing this: Symptom: 550 saying you are temporarily blocked from sending due to repeated bad requests. Use this skill when you run into "SendGrid 550 temporarily blocked: too many bad requests in a short window".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

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