4007: Messaging service reported a send failure

The underlying messaging service rejected or failed the send. Delivered asynchronously as a message.failed webhook. Unlike a timeout, the service actively reported that this message did not go out. Failures of this class were previously reported under the generic 4001.

• Retry the message; transient service-side failures are common
• Verify the recipient address is valid and reachable
• If failures persist for one recipient, try a different preferred_service