Response Codes

SMTP2GO uses conventional HTTP response codes to indicate the success or failure of a request.

In general, codes in the 2xx range indicate success. Codes in the 4xx range indicate an error and reasons the request may have failed are given in the information provided. Codes in the 5xx range indicate an error with SMTP2GO's servers (these are rare and if encountered please contact support for assistance).

Below is a list of status codes and their corresponding definitions:

Status Codes

Status CodeDefinition
200 - OKEverything worked as expected.
400 - Bad RequestThe request was unacceptable, often due to missing a required parameter.
401 - UnauthorizedNo valid API key was provided.
402 - Request FailedThe parameters were valid but the request failed.
403 - ForbiddenThe API key doesn't have permission to perform the request.
404 - Not FoundThe requested resource doesn't exist.
429 - Too Many RequestsToo many requests hit the API too quickly. We recommend an exponential backoff of your requests.
500, 502, 503, 504 - Server ErrorsSomething went wrong on SMTP2GO's end (these are rare).

Additional information is contained in the response body, as in the following examples

   "error": "Failed to remove the single sender email - An error occurred deleting sender email [email protected] or it doesn't exist",
   "error_code": "E_ApiResponseCodes.API_EXCEPTION"

Error Codes

Some errors contain additional field validation error information, as below.

   "error": "An error occurred processing the json data you sent with the request, please make sure the data conforms to the specification for this call (see the documentation here: and try again. Don't forget to set Content-Type to 'application/json'.",
   "error_code": "E_ApiResponseCodes.NON_VALIDATING_IN_PAYLOAD",
   "field_validation_errors": {
      "fieldname": "sender",
      "message": "The field 'sender' was expecting a valid RFC-822 formatted email field but found '', Please correct your JSON payload and try again."

For more detailed explanations of common Error Codes when sending, try our Common Sending Errors knowledgebase article or reach out to our support team for assistance.