Some users fequently ask me how to connect to GMail SMTP service with VMime. You have to connect to server using SMTP protocol (not SMTPS), and set the connection.tls property to true to initiate a secured connection using STARTTLS.
The following code is known to work:
vmime::utility::url url("smtp://smtp.gmail.com");
vmime::ref tr = session->getTransport(url);
tr->setProperty("connection.tls", true);
tr->setProperty("auth.username", "gmail-login");
tr->setProperty("auth.password", "gmail-password");
tr->setProperty("options.need-authentication", true);
tr->setCertificateVerifier(yourCertificateVerifier);