Comment by _wmd

SNI-enabled browsers send the unencrypted hostname in the initial ClientHello frame. It's the first transaction in the protocol, and it's how the server decides the content of the ServerHello reply. There is no way to detect the ability to avoid SNI, or indeed any sensible and generally useful way to tell if a ServerHello varied according to the ClientHello SNI hostname without probing the server, which entails introducing roundtrips, and disclosing the hostname unencrypted at least once on the wire.