curl / libcurl / API / Examples / smtp-mime.c


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 *                             / __| | | | |_) | |
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 * Copyright (C) Daniel Stenberg, <>, et al.
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 * SPDX-License-Identifier: curl
/* <DESC>
 * Send SMTP mime emails
 * </DESC>
#include <stdio.h>
#include <string.h>
#include <curl/curl.h>
/* This is a simple example showing how to send mime mail using libcurl's SMTP
 * capabilities. For an example of using the multi interface please see
 * smtp-multi.c.
 * Note that this example requires libcurl 7.56.0 or above.
#define FROM    "<>"
#define TO      "<>"
#define CC      "<>"
static const char *headers_text[] = {
  "Date: Tue, 22 Aug 2017 14:08:43 +0100",
  "To: " TO,
  "From: " FROM " (Example User)",
  "Cc: " CC " (Another example User)",
  "Message-ID: <dcd7cb36-11db-487a-9f3a-e652a9458efd@"
  "Subject: example sending a MIME-formatted message",
static const char inline_text[] =
  "This is the inline text message of the email.\r\n"
  "  It could be a lot of lines that would be displayed in an email\r\n"
  "viewer that is not able to handle HTML.\r\n";
static const char inline_html[] =
  "<p>This is the inline <b>HTML</b> message of the email.</p>"
  "<br />\r\n"
  "<p>It could be a lot of HTML data that would be displayed by "
  "email viewers able to handle HTML.</p>"
int main(void)
  CURL *curl;
  CURLcode res = CURLE_OK;
  curl = curl_easy_init();
  if(curl) {
    struct curl_slist *headers = NULL;
    struct curl_slist *recipients = NULL;
    struct curl_slist *slist = NULL;
    curl_mime *mime;
    curl_mime *alt;
    curl_mimepart *part;
    const char **cpp;
    /* This is the URL for your mailserver */
    curl_easy_setopt(curl, CURLOPT_URL, "smtp://");
    /* Note that this option is not strictly required, omitting it results in
     * libcurl sending the MAIL FROM command with empty sender data. All
     * autoresponses should have an empty reverse-path, and should be directed
     * to the address in the reverse-path which triggered them. Otherwise,
     * they could cause an endless loop. See RFC 5321 Section 4.5.5 for more
     * details.
    curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM);
    /* Add two recipients, in this particular case they correspond to the
     * To: and Cc: addressees in the header, but they could be any kind of
     * recipient. */
    recipients = curl_slist_append(recipients, TO);
    recipients = curl_slist_append(recipients, CC);
    curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);
    /* allow one of the recipients to fail and still consider it okay */
    curl_easy_setopt(curl, CURLOPT_MAIL_RCPT_ALLOWFAILS, 1L);
    /* Build and set the message header list. */
    for(cpp = headers_text; *cpp; cpp++)
      headers = curl_slist_append(headers, *cpp);
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
    /* Build the mime message. */
    mime = curl_mime_init(curl);
    /* The inline part is an alternative proposing the html and the text
       versions of the email. */
    alt = curl_mime_init(curl);
    /* HTML message. */
    part = curl_mime_addpart(alt);
    curl_mime_data(part, inline_html, CURL_ZERO_TERMINATED);
    curl_mime_type(part, "text/html");
    /* Text message. */
    part = curl_mime_addpart(alt);
    curl_mime_data(part, inline_text, CURL_ZERO_TERMINATED);
    /* Create the inline part. */
    part = curl_mime_addpart(mime);
    curl_mime_subparts(part, alt);
    curl_mime_type(part, "multipart/alternative");
    slist = curl_slist_append(NULL, "Content-Disposition: inline");
    curl_mime_headers(part, slist, 1);
    /* Add the current source program as an attachment. */
    part = curl_mime_addpart(mime);
    curl_mime_filedata(part, "smtp-mime.c");
    curl_easy_setopt(curl, CURLOPT_MIMEPOST, mime);
    /* Send the message */
    res = curl_easy_perform(curl);
    /* Check for errors */
    if(res != CURLE_OK)
      fprintf(stderr, "curl_easy_perform() failed: %s\n",
    /* Free lists. */
    /* curl does not send the QUIT command until you call cleanup, so you
     * should be able to reuse this connection for additional messages
     * (setting CURLOPT_MAIL_FROM and CURLOPT_MAIL_RCPT as required, and
     * calling curl_easy_perform() again. It may not be a good idea to keep
     * the connection open for a long time though (more than a few minutes may
     * result in the server timing out the connection), and you do want to
     * clean up in the end.
    /* Free multipart message. */
  return (int)res;


This source code example is simplified and ignores return codes and error checks to a large extent. We do this to highlight the libcurl function calls and related options and reduce unrelated code.

A real-world application will of course properly check every return value and exit correctly at the first serious error.