When a user is set up without an email address, and
that user uses the link to send an email message to
the admin, the return address is:
I am not sure if the correct behavior at this point is
to force the user to add his email address to his
profile, or display the email field that is used for
the non logged in user.
A hybrid approach would be to show the email field
(required field) and add a notice that this email
address will become the default email address for the user.