Confirm an email address belonging to a specific user

Privacy is important, and after reading this vulnerability, you will know that Facebook gives privacy a great priority

One link enables me to exploit this vulnerability and got $ 5k. alhamdulilah

Too many emails received from facebook contain link to unsubscribe from notifications :

https://www.facebook.com/o.php?k=AS3fdO_cSPoc5dlMxoE&u=userid&mid=midparameter

I look at html form i see e parameter i add it to the previous link, i notice if email is belonging given user in u parameter the response was normal (including secondary emails ), but if i enter the wrong email i get <this page isn’t available > as response

https://www.facebook.com/o.php?k=AS3fdO_cSPoc5dlMxoE&u=userid&e=email&mid=midparameter

Then I reported the vulnerability,

I received a bounty of 5000$

Thanks facebook security team .

Thanks .