The fast and lightweight async Email client library for Arduino.
This Email client library supports Email sending, reading, searching and appending.
This library supports all 32-bit Arduino devices e.g. STM32, SAMD, ESP32, ESP8266, Raspberry Pi RP2040, and Renesas devices.
The 8-bit Atmel's AVR MCUs are not supported.
This library requires 52k program space (network library excluded) for only SMTP or IMAP feature and 82k for using both SMTP and IMAP features.
To send an Email message, user needs to defined the SMTPClient and SMTPMessage class objects.
The one of SSL client if you are sending Email over SSL/TLS or basic network client should be set for the SMTPClient class constructor.
Note that the SSL client or network client assigned to the SMTPClient class object should be lived in the SMTPClient class object usage scope otherwise the error can be occurred.
The STARTTLS options can be set in the advance usage.
Starting the SMTP server connection first via SMTPClient::connect and providing the required parameters e.g. host, port, domain or IP and SMTPResponseCallback function.
Note that, the following code uses the lambda expression as the SMTPResponseCallback callback in SMTPClient::connect.
The SSL connection mode and await options are set true by default which can be changed via its parameters.
Then authenticate using SMTPClient::authenticate by providing the auth credentials and the type of authentication enum e.g. readymail_auth_password, readymail_auth_access_token and readymail_auth_disabled
Compose your message by setting the SMTPMessage class objects's attributes e.g. sender, recipient, subject, content etc.
Then, calling SMTPClient::send using the composed message to send the message.
The following example code is for ESP32 using it's ESP32 core WiFi.h and WiFiClientSecure.h libraries for network interface and SSL client.
The ENABLE_SMTP macro is required for using SMTPClient and SMTPMessage classes. The ENABLE_DEBUG macro is for allowing the processing information debugging.
#include <Arduino.h>
#include <WiFi.h>
#include <WiFiClientSecure.h>
#define ENABLE_SMTP
#define ENABLE_DEBUG
#include "ReadyMail.h"
WiFiClientSecure ssl_client;
SMTPClient smtp(ssl_client);
ssl_client.setInsecure();
// WiFi or network connection here
// ...
// ...
auto statusCallback = [](SMTPStatus status){ Serial.println(status.text);}
smtp.connect("smtp host here", 465, "127.0.0.1", statusCallback);
if (smtp.isConnected())
{
smtp.authenticate("sender email here", "sender email password here", readymail_auth_password);
if (smtp.isAuthenticated())
{
SMTPMessage msg;
msg.sender.name = "ReadyMail";
msg.sender.email = "sender email here";
msg.subject = "Greeting message";
msg.addRecipient("User", "recipient email here");
msg.text.content = "Hello";
msg.html.content = "<html><body>Hello</body></html>";
// Set the message date, select one
msg.timestamp = 1744951350; // The UNIX timestamp (seconds since Midnight Jan 1, 1970)
// msg.date = "Fri, 18 Apr 2025 11:42:30 +0300"; //
// msg.addHeader("Date: Fri, 18 Apr 2025 11:42:30 +0300");
smtp.send(msg);
}
}This library does not set the date header to SMTP message automatically unless system time was set in ESP8266 and ESP32 devices.
User needs to set the message date by one of the following methods before sending the SMTP message.
Providing the RFC 2822 Date haeader using SMTPMessage::addHeader("Date: ?????") or using SMTPMessage::date with RFC 2822 date string or using SMTPMessage::timestamp with the UNIX timestamp.
For ESP8266 and ESP32 devices as mentioned above the message date header will be auto-set, if the device system time was already set before sending the message.
To receive or fetch the Email, only IMAPClient calss object is required. The received message will not store in device memory but redirects to the callback function (IMAPCallbackData) for user processing.
This requires less memory than storing the message. The little memory is required for the chunked buffer that sent to the user callback function.
User can compile or store the message by himself.
When the FileCallback function was assigned to the IMAPClient::fetch or IMAPClient::fetchUID function, the content will be downloaded as files automatically.
The user can limit the size of parts (text, message, application, audio and video) content to be ignored from download and redirect to IMAPCallbackData.
The processes for server connection and authentication or IMAPClient are the same as SMTPClient except for no doman or IP requires in the IMAPClient::connect method.
The mailbox must be selected before fetching or working with its messages.
#include <Arduino.h>
#include <WiFi.h>
#include <WiFiClientSecure.h>
#define ENABLE_IMAP
#define ENABLE_DEBUG
#include "ReadyMail.h"
WiFiClientSecure ssl_client;
IMAPClient imap(ssl_client);
ssl_client.setInsecure();
// WiFi or network connection here
// ...
// ...
auto statusCallback = [](IMAPStatus status){ Serial.println(status.text);}
auto dataCallback = [](IMAPCallbackData data)
{
if (data.isEnvelope) // For showing message headers.
{
for (size_t i = 0; i < data.header.size(); i++)
ReadyMail.printf("%s: %s\n%s", data.header[i].first.c_str(), data.header[i].second.c_str(), (i == data.header.size() - 1 ? "\n" : ""));
}
};
imap.connect("imap host here", 993, statusCallback);
if (smtp.isConnected())
{
smtp.authenticate("sender email here", "sender email password here", readymail_auth_password);
if (smtp.isAuthenticated())
{
imap.list(); // Optional. List all mailboxes.
imap.select("INBOX"); // Select the mailbox to fetch its message.
imap.fetch(imap.getMailbox().msgCount, dataCallback, NULL /* FileCallback */);
}
}The more features usages are available in examples folder.
Click here for all devices usage.
If user's Arduino boards have buit-in WiFi module or already equiped with WiFi capable MCUs, the platform's core SDK WiFi and netwowk (WiFi) SSL client libraries are needed.
#include <WiFi.h>
#include <WiFiClientSecure.h>
WiFiClientSecure ssl_client;#include <ESP8266WiFi.h>
#include <WiFiClientSecure.h>
WiFiClientSecure ssl_client;#include <WiFi.h>
#include <WiFiClientSecure.h>
WiFiClientSecure ssl_client;Arduino® MKR WiFi 1010, Arduino® Nano 33 IoT, Arduino® MKR Vidor 4000
#include <WiFiNINA.h>
WiFiSSLClient ssl_client;#include <WiFi101.h>
WiFiSSLClient ssl_client;#include <WiFiS3.h>
#include <WiFiSSLClient.h>
WiFiSSLClient ssl_client;Arduino® GIGA R1 WiFi, Arduino® OPTA etc.
#include <WiFi.h>
#include <WiFiSSLClient.h>
WiFiSSLClient ssl_client;#include <ETH.h>
#include <WiFiClientSecure.h>
WiFiClientSecure ssl_client;To connect to the network, see Ethernet examples
#include <LwipEthernet.h>
// https://github.com/mobizt/ESP_SSLClient
#include <ESP_SSLClient.h>
Wiznet5500lwIP eth(16 /* Chip select pin */);
WiFiClient basic_client;
ESP_SSLClient ssl_client;To connect to the network, see this example
To set up SSL client, see Set Up ESP_SSLClient.
#include <SPI.h>
// https://github.com/PaulStoffregen/Ethernet
#include <Ethernet.h>
// https://github.com/mobizt/ESP_SSLClient
#include <ESP_SSLClient.h>
EthernetClient basic_client;
ESP_SSLClient ssl_client;To connect to the network, see this example
To set up SSL client, see Set Up ESP_SSLClient.
#include <Ethernet.h>
// https://github.com/mobizt/ESP_SSLClient
#include <ESP_SSLClient.h>
EthernetClient basic_client;
ESP_SSLClient ssl_client;To set up SSL client, see Set Up ESP_SSLClient.
// https://github.com/vshymanskyy/TinyGSM
#include <TinyGsmClient.h>
// https://github.com/mobizt/ESP_SSLClient
#include <ESP_SSLClient.h>
TinyGsm modem(SerialAT);
TinyGsmClient basic_client;
ESP_SSLClient ssl_client;To connect to the network, see this example
To set up SSL client, see Set Up ESP_SSLClient.
#include <PPP.h>
#include <WiFiClientSecure.h>
WiFiClientSecure ssl_client;To connect to the network, see this example
If ESP_SSLClient library was used in some device that uses external network module e.g. STM32 and Teensy or when STARTTLS protocol is needed, the network client e.g. basic Arduino client sould be assigned.
Some options e.g. insecure connection (server SSL certificate skipping) and protocol upgrades are available.
To start using with no SSL certificate, ESP_SSLClient::setInsecure() should be set.
ssl_client.setClient(&basic_client);
ssl_client.setInsecure();The ESP_SSLClient library requires 85k program space.
For using both SMTP and IMAP features with ESP_SSLClient will take approx. 170k program space.
The MIT License (MIT)
Copyright (c) 2025 K. Suwatchai (Mobizt)
Permission is hereby granted, free of charge, to any person returning a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.