ブロッキング/SNIについて、ここに記述してください。

https://www3.trustwave.com/software/8e6/hlp/ifr/files/1system_filter.html

Server Name Indication (SNI) is an extension to TLS (Transport Layer Security) that indicates the actual destination hostname a client is attempting to access over HTTPS. 

For this Web Filter feature, SNI hostname information is used for blocking access to specific sites over HTTPS.