How to send Emails to Gmail using an ESP32 PLC

If you intend to secure the connection between the PLC and the SMTP server, you will also need to install the SSLClient library, which will encrypt the TCP traffic between you and the SMTP server. Even if you use Gmail as the SMTP server, Google forces the connections to be encrypted, so you will also need the library. This library can also be installed with the Library Manager, following the same steps for installing the EMailSender library.

After the installation, if you want to enable SSL in EMailSender, you will need to follow multiple steps:

1. Change the line 469 in the SSLClient.h file from "unsigned char m_iobuf[2048];" to "unsigned char m_iobuf[BR_SSL_BUFSIZE_BIDI];". You can find this file in your Arduino libraries directory, inside the SSLClient/src folder.

2. Put "define SSLCLIENT_WRAPPER " in the EMailSenderKey.h right after "#define EMailSenderKey_h ".

/*
 * Modified simple esp32 Gmail send example
 */

#include "Arduino.h"
#include <EMailSender.h>

#define SENDER_EMAIL "[email protected]"
#define SENDER_PASSWORD "<YOUR-GMAIL-PASSWD>"
#define RECEIVER_EMAIL "[email protected]"
//#define USE_ETH

EMailSender emailSend(SENDER_EMAIL, SENDER_PASSWORD);

#ifndef USE_ETH
#include <WiFi.h>
const char* ssid = "<YOUR-SSID>";
const char* password = "<YOUR-PASSWD>";
uint8_t connection_state = 0;
uint16_t reconnect_interval = 10000;

uint8_t WiFiConnect(const char* nSSID = nullptr, const char* nPassword = nullptr) {
    static uint16_t attempt = 0;
    Serial.print("Connecting to ");
    if(nSSID) {
        WiFi.begin(nSSID, nPassword);
        Serial.println(nSSID);
    }

    uint8_t i = 0;
    while(WiFi.status()!= WL_CONNECTED && i++ < 50) {
        delay(200);
        Serial.print(".");
    }
    ++attempt;
    Serial.println("");
    if(i == 51) {
        Serial.print("Connection: TIMEOUT on attempt: ");
        Serial.println(attempt);
        if(attempt % 2 == 0)
            Serial.println("Check if access point available or SSID and Password\r\n");
        return false;
    }
    Serial.println("Connection: ESTABLISHED");
    Serial.print("Got IP address: ");
    Serial.println(WiFi.localIP());
    return true;
}

void Awaits() {
    uint32_t ts = millis();
    while(!connection_state) {
        delay(50);
        if(millis() > (ts + reconnect_interval) && !connection_state) {
            connection_state = WiFiConnect();
            ts = millis();
        }
    }
}
#endif

void setup() {
    Serial.begin(115200);

#ifdef USE_ETH
    uint8_t mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xEE };
    Ethernet.begin(mac);
#else
    connection_state = WiFiConnect(ssid, password);
    if(!connection_state)  // if not connected to WIFI
        Awaits();          // constantly trying to connect
#endif

    EMailSender::EMailMessage message;
    message.subject = "Hello";
    message.message = "Come to www.industrialshields.com";

    EMailSender::Response resp = emailSend.send(RECEIVER_EMAIL, message);

    Serial.println("Sending status: ");

    Serial.println(resp.status);
    Serial.println(resp.code);
    Serial.println(resp.desc);
}

void loop() {}