The remote web server is affected by a command injection vulnerability.
According to the self-reported version in the server response header, the version of nginx installed on the remote host is 1.5.6 or higher, 1.6.x prior to 1.6.1, or 1.7.x prior to 1.7.4. It is, therefore, affected by a command injection vulnerability. A flaw exists in the function 'ngx_mail_smtp_starttls' within the file 'src/mail/ngx_mail_smtp_handler.c' whereby input to the STARTTLS command is not properly sanitized. This could allow a remote attacker in a privileged network position to obtain sensitive information by injecting commands into an SSL session. Note that this issue is exploitable only when nginx is used as an SMTP proxy.
Apply the patch manually, or upgrade to nginx 1.6.1 / 1.7.4 or later.