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smtplib

smtplib is a simple SMTP mail sending library based on Asio, supporting both synchronous and coroutine-based asynchronous interfaces, and supports SSL/TLS and STARTTLS.

Build & Install

git clone https://github.com/Cra3z/smtplib.git
cd smtplib
mkdir <your-build-dir>
cmake -S . -B <your-build-dir> -DSMTPLIB_EXAMPLES=ON
cmake --build <your-build-dir>
cmake --install <your-build-dir> --prefix <your-install-dir>

The following two variables determine whether to use Boost.Asio or standalone Asio, and whether to use std::format or fmt::format:

• SMTPLIB_USE_BOOST_ASIO: Use Boost.Asio
• SMTPLIB_USE_FMT_FORMAT: Use the fmt library for formatting

For example:

cmake -S . -B <your-build-dir> -DSMTPLIB_EXAMPLES=ON -DSMTPLIB_USE_BOOST_ASIO=ON -DSMTPLIB_USE_FMT_FORMAT=OFF

This will use Boost.Asio and std::format.

smtplib is a header-only library, so you can simply copy smtplib.h to where you need it.
However, it is recommended to embed smtplib as a subproject in your project, or install it first and then import it via CMake's find_package.

Build Requirements

• CMake >= 3.26
• C++17 or newer (C++20 is used by default)

Dependencies

• Boost.Asio >= 1.87 or standalone Asio >= 1.28
• openssl >= 0.9.8
• fmt >= 10.1 (optional, not needed if std::format is available)

Examples

Synchronous send with SSL:

smtplib::net::io_context io_context;
smtplib::client cli{
    io_context.get_executor(),
    "your email",
    "password",
    smtplib::security::ssl
};
cli.connect("smtp.example.com", 465);
cli.send({
    .from = "your email",
    .to = "target email",
    .subject = "Test",
    .body = "Hello!"
});

Asynchronous send (C++20 coroutine) with STARTTLS:

smtplib::net::io_context io_context;
smtplib::client cli{
    io_context.get_executor(),
    "your email",
    "password",
    smtplib::security::starttls
};
smtplib::net::co_spawn(
    io_context,
    [&]() -> smtplib::net::awaitable<void> {
        co_await cli.async_connect("smtp.example.com", 587);
        co_await cli.async_send({
            .from = "your email",
            .to = "target email",
            .subject = "Test",
            .body = "Hello!"
        });
    },
    [](std::exception_ptr exp) {
        try {
            if (exp) {
                std::rethrow_exception(exp);
            }
        }
        catch (const std::exception& ex) {
            std::cerr << "[ERROR] " << ex.what() << std::endl;
        }
    }
);
io_context.run();