title: PHP - Swiftmailer using STARTTLS and self signed certificates
body: <p>I'm trying to send an email with php and swiftmailer, using STARTTLS, but I'm getting a certificate error. I have root access to the SMTP server, and the certificate used is self-signed.
  I'm using Debian on both machines (web server and smtp server)</p>
  
  <p><code>PHP message: PHP Warning:  stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL Error messages:
  error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed in [..]/lib/classes/Swift/Transport/StreamBuffer.php on line 97
  PHP message: PHP Fatal error:  Uncaught exception 'Swift_TransportException' with message 'Unable to connect with TLS encryption' in [..]/lib/classes/Swift/Transport/EsmtpTransport.php:294
  </code></p>
  
  <p>Do I need to add my own certificate somewhere to get it accepted? Or is this some OpenSSL configuration error?</p>