Understanding HTTP status codes can help diagnose issues in email marketing campaigns:
200 OK: The request was successful. 301 Moved Permanently: The resource has been moved to a new URL. 400 Bad Request: The server could not understand the request due to invalid syntax. 401 Unauthorized: Authentication is required and has failed or has not yet been provided. 404 Not Found: The server cannot find the requested resource. 500 Internal Server Error: The server encountered an unexpected condition.