Email sending problem

Hello forum member,

i have a small problem which occur when i send a mail from my account via Gmail.my code is below and when i sending it  an error display that is,

"Failure sending mail".how i slove it?

 my code is,
Dim loginInfo As New NetworkCredential("myaccount@gmail.com", "mypassword")
Dim msg As New MailMessage(EmailFromTextBox.Text, EmailToTextBox.Text, EmailSubject ...