There is something not quite right with this. Can anyone help?
I want to say that if the email textbox is not empty, then do the Email validation, which does work on its own. It is part of a function.
There is something wrong with the first if....???
if (!(document.frmRegister.email.value.length = 0))
messagebox += "You must enter a valid Email address, please try again \n";
You test your code extensively; and
You are ready and able to monitor the IANA list and keep your code up to date;