sending an email with libcurl/smtp with gmail: login denied

Question

I know there are hundreds of posts out there but somehow this does not work for me. I am trying to send an email with libcurl. This is my code:

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

#define FROM    "<[email protected]>"
#define TO      "<[email protected]>"
#define CC      "<[email protected]>"

static const char *payload_text[] = {
  "Date: Mon, 29 Nov 2010 21:54:29 +1100\r\n",
  "To: " TO "\r\n",
  "From: " FROM "(Example User)\r\n",
  "Cc: " CC "(Another example User)\r\n",
  "Message-ID: <dcd7cb36-11db-487a-9f3a-e652a9458efd@"
  "rfcpedant.example.org>\r\n",
  "Subject: SMTP example message\r\n",
  "\r\n", /* empty line to divide headers from body, see RFC5322 */
  "The body of the message starts here.\r\n",
  "\r\n",
  "It could be a lot of lines, could be MIME encoded, whatever.\r\n",
  "Check RFC5322.\r\n",
  NULL
};

struct upload_status {
  int lines_read;
};

static 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((size == 0) || (nmemb == 0) || ((size*nmemb) < 1)) {
    return 0;
  }

  data = 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;

  upload_ctx.lines_read = 0;

  curl = curl_easy_init();
  if(curl) {
    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, "[email protected]");
    curl_easy_setopt(curl, CURLOPT_PASSWORD, "mypassword");
    curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM);

    recipients = curl_slist_append(recipients, TO);
    recipients = curl_slist_append(recipients, CC);
    curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);

   curl_easy_setopt(curl, CURLOPT_READFUNCTION, payload_source);
curl_easy_setopt(curl, CURLOPT_READDATA, &upload_ctx);
    curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);

    res = curl_easy_perform(curl);

    /* Check for errors */
    if(res != CURLE_OK)
      fprintf(stderr, "curl_easy_perform() failed: %s\n",
              curl_easy_strerror(res));

    curl_slist_free_all(recipients);

    curl_easy_cleanup(curl);
  }

  return (int)res;
}

I also tried this example which is very similar except the text gets piped through a different file.

But I always get

curl_easy_perform() failed: Login denied

and then gmail sends me a message saying that someone tried to hack into my account. (login credentials are correct)

This curl-config --feature

gives me

SSL IPv6 UnixSockets libz NTLM NTLM_WB

Reading a couple of blogposts I also tried with hotmail using smtp://smtp.live.com:465

But here I get

curl_easy_perform() failed: Couldn't connect to server

What am I doing wrong here?

Answer 1

I had to spend a great deal of time to get this to work but I finally got it to work. Here's what I found:

First:

#define FROM    "<[email protected]>"
#define TO      "<[email protected]>"
#define CC      "<[email protected]>"

There should not be any "<" or ">" in the email adress. I did the mistake of reusing the defines and could not for my life understand why the login failed.

Second:

You will most likely need to go here and allow unsecure apps: https://www.google.com/settings/security/lesssecureapps

Third:

If you're using port 587 you will need the following line:

curl_easy_setopt(m_curl, CURLOPT_USE_SSL, CURLUSESSL_ALL);

This does not seem to be needed for 465.

Note:

It's ok to use either port 465 or 587. 465 requires SSL so you will need to use smtps instead of smtp to specify this - smtps://smtp.gmail.com:465. I found some info about it here: https://support.google.com/a/answer/176600?hl=en

Answer 2

In 2022, you need to create a App Password on you google account. And then using this password you can send the emails without problem.

Take a look on this link: https://support.google.com/mail/answer/185833?hl=en