code: public ApiResponse<Integer> postCharactersCharacterIdMailLabelsWithHttpInfo(Integer characterId, String datasource,
              String token, MailLabelSimple mailLabelSimple) throws ApiException {
          com.squareup.okhttp.Call call = postCharactersCharacterIdMailLabelsValidateBeforeCall(characterId, datasource,
                  token, mailLabelSimple, null);
          Type localVarReturnType = new TypeToken<Integer>() {
          }.getType();
          return apiClient.execute(call, localVarReturnType);
      }
docs: Create a mail label Create a mail label --- SSO Scope:
  esi-mail.organize_mail.v1
  
  @param characterId
  An EVE character ID (required)
  @param datasource
  The server name you would like data from (optional, default to
  tranquility)
  @param token
  Access token to use if unable to set a header (optional)
  @param mailLabelSimple
  (optional)
  @return ApiResponse&lt;Integer&gt;
  @throws ApiException
  If fail to call the API, e.g. server error or cannot
  deserialize the response body