To protect or not email attribute of user

Hi,

What's your best practice about the email attribute of a registered user
in your DB. I don't want people to be able to change email.

But what's best?

1) protect the email attribute with attr_protected or attr_accessible
and suffer the pain of having to do user.email = .... everywhere in your
code and tests

2) Keep email accessible, but write a custom update_attributes that
filters the email attribute?