send email C++ libcurl SMTPS

Question

I'm trying to write a simple C++ code that sends an email to another address with libcurl. I wrote this, which compiles correctly, but I run it and get the message: Error: Problem with the local SSL certificate (58)

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

int main() {
     // Creating the message
     std::string from = "[email protected]";
     std::string to = "[email protected]";
     std::string password = "password";
     std::string subject = "Object";
     std::string body = "This is may message\n";

     // Configuring cURL
     CURL *curl;
     CURLcode res = CURLE_OK;

     curl_global_init(CURL_GLOBAL_DEFAULT);
     curl = curl_easy_init();

     if(curl) {
         // Configuration of the recipient, sender, subject and body of the message
         struct curl_slist *recipients = NULL;
         recipients = curl_slist_append(recipients, ("To: " + to).c_str());
         recipients = curl_slist_append(recipients, ("From: " + from).c_str());
         recipients = curl_slist_append(recipients, ("Subject: " + subject).c_str());

// Configuring cURL options
         curl_easy_setopt(curl, CURLOPT_URL, "smtps://authsmtp.securemail.pro:465");
         curl_easy_setopt(curl, CURLOPT_USE_SSL, CURLUSESSL_ALL);
         curl_easy_setopt(curl, CURLOPT_MAIL_FROM, from.c_str());
         curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);
         curl_easy_setopt(curl, CURLOPT_USERNAME, from.c_str());
         curl_easy_setopt(curl, CURLOPT_PASSWORD, password.c_str());
         curl_easy_setopt(curl, CURLOPT_SSL_VERIFYSTATUS, 1L);
         curl_easy_setopt(curl, CURLOPT_CAPATH, "/etc/ssl/certs");
         curl_easy_setopt(curl, CURLOPT_SSLCERT, "/etc/ssl/certs/ca-certificates.crt");
         // Sending the message body
         curl_easy_setopt(curl, CURLOPT_READFUNCTION, NULL);
         curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
         curl_easy_setopt(curl, CURLOPT_READDATA, body.c_str());

         // Executing the request
         res = curl_easy_perform(curl);

         // Cleaning and closing
         curl_slist_free_all(recipients);
         curl_easy_cleanup(curl);
     }

     // Error handling
     if(res != CURLE_OK)
         std::cerr << "Error: " << curl_easy_strerror(res) << " (" << res << ")"<< std::endl;

     curl_global_cleanup();

     return 0;

I attempted to send with curl with the following command: curl smtps://authsmtp.securemail.pro:465 -v --mail-from "[email protected]" --mail-rcpt "[email protected]" --ssl -u [email protected]:password -T "test.txt" -k --anyauth

EXTRACT OF THE RESULT

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0*   Trying 81.88.48.66:465...
* Connected to authsmtp.securemail.pro (81.88.48.66) port 465 (#0)
* successfully set certificate verify locations:
*  CAfile: /etc/ssl/certs/ca-certificates.crt
*  CApath: /etc/ssl/certs

* Server certificate:
*  subject: C=IT; ST=Firenze; O=Register S.p.A.; CN=*.securemail.pro
*  start date: Feb 17 00:00:00 2023 GMT
*  expire date: Mar  3 23:59:59 2024 GMT
*  issuer: C=GB; ST=Greater Manchester; L=Salford; O=Sectigo Limited; CN=Sectigo RSA Organization Validation Secure Server CA
*  SSL certificate verify ok.

< 235 2.7.0 ... authentication succeeded
} [5 bytes data]
> MAIL FROM:<[email protected]> SIZE=13
{ [5 bytes data]
< 250 2.1.0 <[email protected]> sender ok
} [5 bytes data]
> RCPT TO:<[email protected]>
{ [5 bytes data]
< 250 2.1.5 <[email protected]> recipient ok
} [5 bytes data]
> DATA
{ [5 bytes data]
< 354 OK
} [5 bytes data]
* We are completely uploaded and fine
} [5 bytes data]
< 250 2.0.0 WF8GrZuZ7JFspWF8HrHGcu mail accepted for delivery
100    13    0     0  100    13      0     37 --:--:-- --:--:-- --:--:--    37
* Connection #0 to host authsmtp.securemail.pro left intact

On [email protected] I receive mailer-daemon. In my opinion it is a permissions problem but they are the system ones that normally work with Thunderbird I'm trying with Debian 11 and libcurl 7.74, but I also tried in Windows 10 with libcurl 8 and the result is the same