Hi Nisha,
As per checking, login operation for Gmail cannot be controlled by Bluecoat Application Filtering.
Blue Coat#conf t
Blue Coat#(config)content-filter
Blue Coat#(config content-filter)bluecoat
Blue Coat#(config bluecoat)view operations application Gmail
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you can find more in details in below article
https://support.symantec.com/en_US/article.TECH243301.html
In order to block the Gmail login, you must block Gmail login page
Regards,
Jahangir Shaikh