Email in Digital Signature
This is the official VeriSign answer:
Its normal for email address not to appear in the email address filed, the certificate does not validate the organization's email address. The e-mail address always appears as "not available" when viewing properties of signed code. This is because the certificate validates the organization but requires no information about the e-mail address of the organization. Thus, we have validated the organization, but have not validated the e-mail. This in no way lessens the value or usefulness of your ID.
So there you have it...