How to check that this emailID exists or not

Good day all of you.

 

i want to know that how can we chek any particular emailID exists or not.

i mean i build a  SIGNUP form that have user information , user enters here his mailID like bharatvee4@yahoo.co.in it exists because its mine.

but if user enters a emailID that does not exist then how  can we give him message that this is not a existing EmailID. Because if we dont have the way to find out

the existing EmailIDs then our databse will be bearing a lot of unexisting IDS.

Thanks to all of you.

 
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