halt while sending email with Poco Net - c++

Question

I'm trying to send an email using the Poco Net library with this code (my credentials are arbitrary obviously):
void send_email() {
// Poco::Net::SMTPClientSession session("localhost", 465);
const std::string& smtp_host {"mail.example.com"};
const std::string& smtp_user {"marinos#example.com"};
const std::string& smtp_passwd {"myPassword"};
std::string to = "marinos#example.com";
std::string from = "marinos#example.com";
std::string subject = "Your first e-mail message sent using Poco Libraries";
subject = Poco::Net::MailMessage::encodeWord(subject, "UTF-8");
std::string content = "Well done! You've successfully sent your first message using Poco SMTPClientSession";
Poco::Net::MailMessage message;
message.setSender(from);
message.addRecipient(Poco::Net::MailRecipient{Poco::Net::MailRecipient::PRIMARY_RECIPIENT, to});
message.setSubject(subject);
message.setContentType("text/plain; charset=UTF-8");
message.setContent(content, Poco::Net::MailMessage::ENCODING_8BIT);
try {
Poco::Net::SMTPClientSession session(smtp_host, 465);
session.open(); // this is where it halts
try {
session.login(Poco::Net::SMTPClientSession::AUTH_LOGIN, smtp_user, smtp_passwd);
session.sendMessage(message);
std::cout << "Message successfully sent" << std::endl;
session.close();
} catch (Poco::Net::SMTPException& e) {
std::cerr << e.displayText() << std::endl;
session.close();
}
} catch (Poco::Net::NetException& e) {
std::cerr << e.displayText() << std::endl;
}
}
and my program simply halts. I've used a debugger to locate the problem and it seems that the program halts when calling session.open(). Am I doing something wrong here?

Answer 1

Since I do not know specification of your SMTP server, I am speculating that you're probably suppose to use SMTPS instead of plain SMTP, because port 465 is default port for SMTPS (according to Wikipedia). I guess the program halts during SSL handshaking. By looking into Poco documentation I see that there exists SSL version of the Poco::Net::SMTPClientSession. Thus, you should try with SecureSMTPClientSession. Check if your mail server requires START_TLS, in that case I guess you should additionally call bool startTLS().