Sending Email in C++: Libraries and Implementation

Sending Email in C++: Library Overview and Practical Examples

Sending emails is one of the key tasks for many applications: from monitoring and notification systems to full-fledged email clients. The C++ language does not have built-in support for the SMTP protocol, but there are powerful third-party libraries that make it easy to integrate email sending. In this article, we will look at the most popular tools, their installation, and provide working code examples.

Main Ways to Send Email in C++

There are three main approaches to sending emails in C++:

• Using libcurl — the most popular and flexible library. Supports SMTP, SMTP-SSL, SMTP-STARTTLS.
• Using VMime — a specialized library for working with MIME messages, encryption, and attachments.
• Direct socket programming — a low-level approach requiring manual implementation of the SMTP protocol.

In this guide, we will focus on libcurl as the most versatile and widely used solution.

Installing libcurl

To work with SMTP via libcurl, you need to install the library itself and its header files. Examples for different operating systems:

# Ubuntu / Debiansudo apt-get install libcurl4-openssl-dev

# CentOS / Fedorasudo yum install libcurl-devel

# macOS (via Homebrew)brew install curl

# Windows (via vcpkg)vcpkg install curl

Make sure your curl build includes support for SMTP and SSL protocols. You can check this with the command:

curl --version | grep -i smtp

Simple Example: Sending a Text Email

Let's look at a basic example of sending an email via the Gmail SMTP server using libcurl. For successful sending, you will need an App Password for Gmail.

#include <stdio.h>#include <string.h>#include <curl/curl.h>

// Structure for passing email datastruct upload_status {    int lines_read;    const char **payload_text;};

// Callback function for reading the email bodystatic size_t payload_source(void *ptr, size_t size, size_t nmemb, void *userp) {    struct upload_status *upload_ctx = (struct upload_status *)userp;    const char *data;

    if (upload_ctx->lines_read < 5) {        data = upload_ctx->payload_text[upload_ctx->lines_read];        if (data) {            size_t len = strlen(data);            memcpy(ptr, data, len);            upload_ctx->lines_read++;            return len;        }    }    return 0;}

int main(void) {    CURL *curl;    CURLcode res = CURLE_OK;    struct curl_slist *recipients = NULL;    struct upload_status upload_ctx;

    // Email text (each line is a separate element)    const char *payload_text[] = {        "From: Your Name <youremail@gmail.com>\\r",        "To: Recipient <recipient@example.com>\\r",        "Subject: Hello from C++!\\r",        "\\r", // empty line — separator between headers and body        "This is a test email sent using libcurl in C++.\\r",        NULL    };

    upload_ctx.lines_read = 0;    upload_ctx.payload_text = payload_text;

    curl_global_init(CURL_GLOBAL_DEFAULT);    curl = curl_easy_init();

    if (curl) {        // Configuring the Gmail SMTP server        curl_easy_setopt(curl, CURLOPT_URL, "smtp://smtp.gmail.com:587");        curl_easy_setopt(curl, CURLOPT_USE_SSL, CURLUSESSL_ALL);        curl_easy_setopt(curl, CURLOPT_USERNAME, "youremail@gmail.com");        curl_easy_setopt(curl, CURLOPT_PASSWORD, "your_app_password");

        // Specify sender and recipient        curl_easy_setopt(curl, CURLOPT_MAIL_FROM, "<youremail@gmail.com>");        recipients = curl_slist_append(recipients, "<recipie