Rob,
You could try the following JavaScript (which uses a 'regular expression' to define a validation pattern) on the *exit event of your e-mail address field. In this example the email adress 'email' is on the first page of the form which has been named 'Page_01'. The names on your form could well be different.
// Validate the email address.
var e_mail = new RegExp();
// Set the regular expression to look for an email address in general form.
e_mail.compile("^[a-z0-9_\\-\\.]+\\@[a-z0-9_\\-\\.]+\\.[a-z]{2,3}$","i");
// Test the rawValue of the current object to see if it fits the general form of an email address.
if (e_mail.test(email.rawValue) == false)
{xfa.host.messageBox("Please enter a genuine E-mail Adress.","Invalid Information",0);
xfa.host.setFocus("form1.Page_01.email");
}
Regular expressions can look pretty daunting, but are a very powerful JavaScript feature that can prove to be invaluable for setting up data validation criteria. Any JavaScript (or Jscript) reference book or on-line tutorial will have a section showing you how to build them.
Hope this helps,
John