Validate An Email Address In The Server At The Beginning Of The Program To Continue Further?

Imports System.Net
Imports System.Net.Mail
Public Class Form1
Sub sendMail()
Try
Dim AnEmailMessage As New MailMessage

[Code]...

I use this code to send an email through gmail account but the thing I want to do is, I want to check whether the given email and password exists or not and if it exists then pop out a text box with the body of the mail and type the text and then send it as a mail. But in the above code you have to log in and type body and when you send the mail , It verifies for the email and password while sending and if anything goes wrong says there is no such gmail account.but i want to check it whether the email and password exists or not, when the user enters the email and password at the beginning itself.So that he enters the right email to log on to compose a mail.Is there any way to check whether the given email and password is correct at the beginning only ?