Is there a webservice from discountasp to make me able to validate Emails for my domain ?

Dear All,

I am building an application for my company so , Instead of creating users I want to use the Emails as user accounts
so when he login by valid username and password, I will direct him to a special page .

My applicaation just need to send the Username and password
and check if it correct or not.

i.e. consume a webservice that return true or fals.

and I just need that to continue my application .

is this available ?

if not what is the laternative method to do it?

Thanks