c++ libcurl sent smtp mail using github library fails - c++

Question

I am trying to use the code given in this git repository. The code is not mine and I would like to thank honeyligo for his work!
I unfortunately can't manage to run it properly (I had to fix some compilation issues but nothing dramatic).
After setting the main.cpp to
#include <unistd.h>
#include "curlsmtp.h"
int main(){
CurlSmtp* mail = new CurlSmtp(
"MYADDRESS#gmail.com",
"MYPASSWORD",
{ "foo#yahoo.fr" },
{},
{},
{},
"it's a subject",
"hello world you aredfsf",
"smtp.gmail.com",
"465");
mail->send_mail();
sleep(3);
delete mail;
return 0;
}
it constantly returns
* Expire in 200 ms for 1 (transfer 0x558a3b95d7e0)
then fails after a timeout. The code is roughly 500 lines long and well commented but I can't figure out why it fails. I don't know much about curl but I'm looking for a way to automatically sent mails with a pdf attached to my high school students. I need to implement a c++ solution because this will be part of a larger project.
Thanks for your help!

Answer 1

After some testing with curl both from the CLI and in a C app using libcurl, I found the issue: gmail only accepts smtp requests if you explicitly use smtps (smtps://smtp.gmail.com).
As it's hardcoded in this curlsmtp lib to use smtp://, you either modify it (set_curl_option method) or use libcurl directly (an easy example here: https://curl.haxx.se/libcurl/c/smtp-mime.html)
Also, you either have to set up 2FA in your Google account and create an app password, or enable access for less secure apps if there is no 2FA (https://myaccount.google.com/lesssecureapps).