如何使用libcurl发送电子邮件

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

int main(void)
{
    CURL *curl;
    CURLcode res = CURLE_OK;

    curl_global_init(CURL_GLOBAL_DEFAULT);

    curl = curl_easy_init();
    if(curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "smtp://smtp.example.com");
        curl_easy_setopt(curl, CURLOPT_PORT, 587);
        curl_easy_setopt(curl, CURLOPT_MAIL_FROM, "sender@example.com");

        struct curl_slist *recipients = NULL;
        recipients = curl_slist_append(recipients, "recipient1@example.com");
        recipients = curl_slist_append(recipients, "recipient2@example.com");
        curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);

        curl_easy_setopt(curl, CURLOPT_READDATA, fopen("mail.txt", "r"));

        curl_easy_setopt(curl, CURLOPT_USERNAME, "username");
        curl_easy_setopt(curl, CURLOPT_PASSWORD, "password");

        res = curl_easy_perform(curl);

        curl_slist_free_all(recipients);
        curl_easy_cleanup(curl);
    }

    curl_global_cleanup();

    return (int)res;
}