Use this
string email ="^([a-zA-Z0-9_\\-\\.]+)@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.)|(([a-zA-Z0-9\\-]+\\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\\]?)$";
Regex r = new Regex (email);
if (r.IsMatch(txtemailid.Text))
{
return true;
}
else
{
MessageBox.Show("Please Enter proper EmailId"","Employee Form", MessageBoxButtons.OK, MessageBoxIcon.Information);
return false;
}