EMailSender Library v4.1.1

A comprehensive Arduino library for sending emails via SMTP with full support for attachments, multiple recipients, and secure connections (SSL/TLS and STARTTLS).

Author: Renzo Mischianti
Website: www.mischianti.org
GitHub: @xreef

📚 Documentation & Tutorials

Complete tutorials and articles available on mischianti.org:

General Documentation

🌐 EMailSender Library Home - Main library page with all articles
📖 Library Forum & Support - Community support and discussions

Platform-Specific Guides

Advanced Topics

🔐 STARTTLS vs SSL/TLS: Understanding secure email - NEW! Security protocols explained
📮 Gmail App Passwords: Setup guide - Configure Gmail for Arduino
🛠️ Troubleshooting email sending issues - Common problems and solutions

✨ Features

Core Features

✅ Send emails via SMTP with authentication
✅ Multiple recipients (To, Cc, Bcc)
✅ HTML and plain text email formats
✅ File attachments from various storage systems
✅ Base64 encoding for attachments
✅ Custom sender name and email address
✅ Subject and message body customization

Security Features (NEW in v4.0.0)

✅ STARTTLS support (Port 587) - NEW!
✅ Implicit SSL/TLS (Port 465)
✅ Multiple authentication methods:
- AUTH LOGIN (default)
- AUTH PLAIN (SASL)
- CRAM-MD5 (ESP32 only)
✅ Internal SSLClient for STARTTLS on ESP32/ESP8266
✅ OpenSLab SSLClient (BearSSL) for Ethernet shields

Network Support

Multiple network interfaces (WiFi, Ethernet, WiFiNINA)
Automatic IP resolution
Connection retry logic
Flexible client configuration

🎯 Supported Platforms

Platform	WiFi	Ethernet	SSL/TLS	STARTTLS
ESP32	✅	✅	✅	✅
ESP8266	✅	✅	✅	✅
Arduino Mega/Uno	❌	✅	❌	❌
Arduino SAMD	✅	✅	✅	✅
STM32	❌	✅	✅	✅
Raspberry Pi Pico (RP2040)	✅	✅	✅	✅

⚠️ IMPORTANTE - Arduino Mega/Uno e SSL/TLS:

Arduino Mega and Uno DO NOT support SSL/TLS due to severe RAM limitations:

Arduino Mega has only 8KB of RAM

Arduino Uno has only 2KB of RAM

BearSSL for SSL/TLS requires at least 24KB of RAM for encryption buffers

Alternative solutions for Arduino Mega/Uno:

✅ Use non-secure SMTP (port 25) - Works but not recommended

✅ Use a local SMTP relay - Configure a local server that handles SSL

✅ Switch to ESP32/ESP8266 - They have more RAM and native SSL/TLS support

✅ Use Arduino SAMD (MKR WiFi 1010) - Has 32KB RAM and supports SSL/TLS

Arduino Mega/Uno examples in this library use only non-secure SMTP!

🌐 Supported Network Interfaces

WiFi (ESP32/ESP8266) - WiFiClient / WiFiClientSecure
WiFi (SAMD/MBED) - WiFiNINA library
Ethernet W5100/W5200/W5500 - Standard Ethernet library
Ethernet ENC28J60 - UIPEthernet library
Ethernet with SSL - SSLClient wrapper for secure connections

💾 Supported Storage Systems

Internal Storage (Microcontroller Flash)

SPIFFS (ESP32, ESP8266)
LittleFS (ESP32, ESP8266, RP2040)
FFAT (ESP32)
SPIFM (SPI Flash with Adafruit_SPIFlash)
Generic stream and string attachments option

External Storage (SD/microSD Cards)

SD (Standard SD library)
SdFat (Version 1.x for RP2040/ESP8266)
SdFat2 (Version 2.x for modern platforms)

📦 Installation

Arduino IDE

Open Arduino IDE
Go to Sketch > Include Library > Manage Libraries
Search for "EMailSender"
Click Install

PlatformIO

Add to your platformio.ini:

lib_deps = 
    xreef/EMailSender@^4.1.1

Manual Installation

Download the library from GitHub
Extract to Arduino libraries folder
Restart Arduino IDE

🚀 Basic Usage

Simple Email (ESP32 with Gmail)

#include <WiFi.h>
#include <EMailSender.h>

const char* ssid = "YOUR_SSID";
const char* password = "YOUR_PASSWORD";

// Gmail SMTP configuration
EMailSender emailSend("[email protected]", 
                      "your_app_password",
                      "[email protected]", 
                      "Your Name",
                      "smtp.gmail.com", 
                      587);  // Port 587 for STARTTLS

void setup() {
  Serial.begin(115200);
  
  // Connect to WiFi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nWiFi Connected!");
  
  // Prepare email message
  EMailSender::EMailMessage message;
  message.subject = "Test Email";
  message.message = "Hello from ESP32!";
  
  // Send email
  EMailSender::Response resp = emailSend.send("[email protected]", message);
  
  Serial.println("Sending status: ");
  Serial.println(resp.code);
  Serial.println(resp.desc);
  Serial.println(resp.status);
}

void loop() {
  // Nothing here
}

HTML Email with Multiple Recipients

EMailSender::EMailMessage message;
message.subject = "HTML Email Test";
message.message = "<h1>Hello!</h1><p>This is an <b>HTML</b> email.</p>";
message.mime = MIME_TEXT_HTML;  // Set MIME type to HTML

// Multiple recipients
const char* recipients[] = {
  "[email protected]",
  "[email protected]",
  "[email protected]"
};

EMailSender::Response resp = emailSend.send(recipients, 3, message);

Email with CC and BCC

// Array with To, Cc, and Bcc addresses
const char* allRecipients[] = {
  "[email protected]",      // To (1)
  "[email protected]",      // Cc (1)
  "[email protected]"      // Bcc (1)
};

// send(recipients, numTo, numCc, numBcc, message)
EMailSender::Response resp = emailSend.send(allRecipients, 1, 1, 1, message);

Debug Mode

Enable debugging by uncommenting in EMailSenderKey.h:

#define EMAIL_SENDER_DEBUG
#define DEBUG_PRINTER Serial

This will print detailed SMTP communication to Serial Monitor.

Memory Issues

For boards with limited RAM (like Arduino Uno):

Disable attachments if not needed
Use smaller email messages
Consider using Arduino Mega or ESP32

Gmail Specific Issues

"Username and Password not accepted"

Enable 2-Factor Authentication
Generate App Password at https://myaccount.google.com/apppasswords
Use the 16-character app password (no spaces)

"Less secure app access"

Google removed "less secure apps" option
You MUST use App Passwords now
Regular account password will not work

Change log v4.x

10/11/2025: v4.1.1
- Minor enhancements: add support for Stream and String attachments improvements
- Bug fixes: edge-case encoding issues and small fixes in attachment handling
10/11/2025: v4.1.0
- Add Stream and File as attachement type
- Bug fix for size and encoding
09/10/2025: v4.0.1 Fix path sslclient and code completition of Platformio

📝 Changelog v4.0.0 - 08/10/2025

New Features

✨ STARTTLS support (Port 587) - Full implementation for secure email on port 587
✨ Internal SSLClient integration - Built-in SSL/TLS support for ESP32/ESP8266
✨ Enhanced authentication - Better support for various SMTP auth methods
✨ Improved error handling - More detailed error messages and responses

Improvements

🔧 Unified client handling for better compatibility
🔧 Better SSL/TLS handshake management
🔧 Improved EHLO/HELO command handling with multi-line response support
🔧 Enhanced connection retry logic
🔧 Better memory management for large attachments

Bug Fixes

🐛 Fixed SSLClient initialization on ESP32
🐛 Fixed STARTTLS upgrade sequence
🐛 Corrected client scope issues
🐛 Fixed BearSSL integration for Ethernet shields

Breaking Changes

⚠️ Minimum Arduino IDE version: 1.8.x
⚠️ ESP32 core minimum version: 2.0.x (for WiFiClientSecure improvements)
⚠️ Some internal API changes (user-facing API remains compatible)

Migration from v3.x

Most code will work without changes. If using custom client configuration:

Check EMailSenderKey.h for new defines
Update authentication methods if using advanced features
Test STARTTLS connections (port 587) for better security

Change log v3.x

14/03/2024: v3.0.14 Support Arduino GIGA WiFi
31/10/2023: v3.0.13 Fix wrong implementation of FORCE_DISABLE_SSL
17/10/2023: v3.0.12 Fix warnigs of variable not used #43 thanks to @Patriboom @Andy2015
16/02/2023: v3.0.11 Add support for Ethernet_Generic
20/01/2023: v3.0.10 Add the management of ESP8266SdFat library on Raspberry Pi Pico #forum
17/01/2023: v3.0.10 Add the mamagement of auto check of response number #36 thanks to @HACKER-3000 @H3
13/01/2023: v3.0.9 Fix external storage error 404 (#forum
05/01/2023: v3.0.8 Fix distribution list examples
22/09/2022: v3.0.7 Add Raspberry Pi Pico W and rp2040 boards
20/09/2022: v3.0.7 Add STM32 management for https://github.com/rogerclarkmelbourne/Arduino_STM32 library.
16/08/2022: v3.0.6 Add FORCE_DISABLE_SSL to disable SSL if present
19/07/2022: v3.0.5 Additional fix on additional response management (#26)
12/07/2022: v3.0.4 Fixed attachment issue on SPIFFS and LittleFS
06/07/2022: v3.0.3 Manage multiple response message after connect and HELO (#26)
03/06/2022: v3.0.2 Add possibility to set additionalResponseLineOnConnection with void setAdditionalResponseLineOnConnection(uint8_t numLines = 0), needed if on connection you receive 220 response as error, and add Ethernet2.
20/05/2022: v3.0.1 Put inside scope the client declaration (if you don't use SSLClient) for backward compatibility
18/05/2022: v3.0.0 Add STM32 support. Add SSLClient integration to allow send Email with SSL encryption (like Gmail) with ethernet (tested with STM32, ESP32, w5500, and enc28j60), minor fix
12/04/2021: v2.4.3 Fix multiple email send
12/04/2021: v2.4.1 Add support for LITTLEFS and Ffat on esp32 and fix certificate verification from esp32 core 1.0.5
18/03/2021: v2.3.0 Add support for LittleFS on esp8266
02/01/2021: v2.2.0 New support for SAMD devices via WiFiNINA (Arduino MKR WiFi 1010, Arduino Vidor 4000 and Arduino UNO WiFi Rev.2 ecc.).
01/01/2021: v2.1.5 Add possibility to use EHLO instead of HELO, and SASL login.
27/11/2020: v2.1.4 Add more constructor to allow more structure for distribution list (now const char*, char* and String array are supported)

📄 License

MIT License - See LICENSE file for details

🤝 Contributing

Contributions are welcome! Please:

Fork the repository
Create a feature branch
Commit your changes
Push to the branch
Create a Pull Request

📞 Support

Website: https://www.mischianti.org
GitHub Issues: https://github.com/xreef/EMailSender/issues
Forum: https://www.mischianti.org/forums/

👤 Author

Renzo Mischianti

⭐ Show Your Support

If this library helped your project, please ⭐ star it on GitHub!

Made with ❤️ by Renzo Mischianti

Name		Name	Last commit message	Last commit date
Latest commit History 133 Commits
examples		examples
resources		resources
src		src
.project		.project
EMailSender.h		EMailSender.h
LICENSE		LICENSE
README.md		README.md
keywords.txt		keywords.txt
library.json		library.json
library.properties		library.properties

License

xreef/EMailSender

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EMailSender Library v4.1.1

📚 Documentation & Tutorials

General Documentation

Platform-Specific Guides

ESP32 Tutorials

ESP8266 Tutorials

Arduino Tutorials

STM32 Tutorials

Raspberry Pi Pico (RP2040) Tutorials

Advanced Topics

📋 Table of Contents

✨ Features

Core Features

Security Features (NEW in v4.0.0)

Network Support

🎯 Supported Platforms

🌐 Supported Network Interfaces

💾 Supported Storage Systems

Internal Storage (Microcontroller Flash)

External Storage (SD/microSD Cards)

📦 Installation

Arduino IDE

PlatformIO

Manual Installation

🚀 Basic Usage

Simple Email (ESP32 with Gmail)

HTML Email with Multiple Recipients

Email with CC and BCC

Debug Mode

Memory Issues

Gmail Specific Issues

Change log v4.x

📝 Changelog v4.0.0 - 08/10/2025

New Features

Improvements

Bug Fixes

Breaking Changes

Migration from v3.x

Change log v3.x

📄 License

🤝 Contributing

📞 Support

👤 Author

⭐ Show Your Support

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