ESP-WROOM-02(ESP8266)でメールが送れる!?のスケッチ公開！

#include <ESP8266WiFi.h>
const char* ssid = "SSID";
const char* password = "パスワード";
const char* host = "ドメイン";
const char* auth_pass = "ユーザー名\0ユーザー名\0メールパスワード";
const char* mail_from = "差出人のメールアドレス";
const char* rcpt_to = "宛先のメールアドレス";
const char* subj = "ESP-WROOM-02からテストメール";
const int httpPort = 587;　//SMTPサーバーがポート587を使っている場合
int value = 0;
WiFiClient client;
void ReadLoop(){
    while(client.available()){
      String line = client.readStringUntil('\r');
      Serial.print(line);
    }
}
void setup() {
  Serial.begin(115200);
  delay(10);
// We start by connecting to a WiFi network
  Serial.println();
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}
void loop() {
  if (Serial.available() > 0) {
    byte inByte = Serial.read();
    if (inByte == 'S')
    {
      delay(5000);
      ++value;
      Serial.print("connecting to ");
      Serial.println(host);
// Use WiFiClient class to create TCP connections
     if (!client.connect(host, httpPort)) {
       Serial.println("connection failed");
       return;
     }
    client.print("ehlo ");
    client.println(host);
    ReadLoop();
    delay(1000);
    client.println("AUTH PLAIN");
    ReadLoop();
    delay(3000);
    client.println(auth_pass);
    ReadLoop();
    delay(1000);
    client.print("mail from:");
    client.println(mail_from);
    ReadLoop();
    delay(1000);
    client.print("rcpt to:");
    client.println(rcpt_to);
    ReadLoop();
    delay(1000);
    client.println("data");
    ReadLoop();
    delay(1000);
    client.print("From:");
    client.println(mail_from);
    ReadLoop();
    delay(1000);
    client.print("To:");
    client.println(rcpt_to);
    ReadLoop();
    delay(1000);
    client.print("subject:");
    client.println(subj);
    ReadLoop();
    delay(1000);
    client.println("");
    client.println("メールのテスト送信ですよ～");
    ReadLoop();
    delay(1000);
    client.println(".");
    ReadLoop();
    delay(1000);
    client.println("quit");
    ReadLoop();
    Serial.println();
    Serial.println("closing connection");
    }
  }
}