class Net::SMTP

def enable_tls(context = nil)

to have any effect. +context+ is a OpenSSL::SSL::SSLContext object.
this object. Must be called before the connection is established
Enables SMTP/TLS (SMTPS: SMTP over direct TLS connection) for 
def enable_tls(context = nil)
  raise 'openssl library not installed' unless defined?(OpenSSL::VERSION)
  raise ArgumentError, "SMTPS and STARTTLS is exclusive" if @starttls == :always
  @tls = true
  @ssl_context_tls = context
end