In case you are having problems to configure Roundcube to send mail, please note the following:
If you are connecting on port 587 you should probably use
tls://mail.mydomain.org instead of
ssl://mail.mydomain.org because (by default) STARTTLS is used on port 587. In case you are using port 465 you should use the
ssl:// prefix, because this is the default port for SSL.