validate email address
public bool IsValid(string emailaddress)
{
private const string EmailRegEx = @"^[w!#$%&'*+-/=?^_`{|}~]+(.[w!#$%&'*+-/=?^_`{|}~]+)*"
+ "@"
+ @"((([w]+([-w]*[w]+)*.)+[a-zA-Z]+)|"
+ @"((([01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5]).){3}[01]?[0-9]{1,2}|2[0-4][0-9]|25[0-5]))z";
return new Regex(EmailRegEx, RegexOptions.None).Match(emailaddress).Success;
}