The disabled status is a bit different. I'm guessing that you mean that if an email is disabled, Mahara should not send a message to it. But it probably makes more sense that users can say "send me e-mail or never send me email", and not think about which addresses are disabled or not, because only one address is ever being sent e-mail anyway - the one that's in the usr table. That's probably something that should be a user account preference, which means it should go in the usr_account_preference table (where it's actually _set_ is another story, it might make sense on the settings page and might make sense on the profile page where the emails are).
Do bounces get returned at email_user() time? I wouldn't think so? I thought that bounces are e-mails sent from the other server, and you have to have a script registered to handle them?
I'm not sure about that roadmap item. It might mean that they don't want students to have to have an e-mail address at all, rather than allowing them to have one that's the same as another user's. As it is, I'm not entirely sure that Mahara's email addresses are checked to be unique at the database level anyway - for example, I think you might be able to sneak an SSO user into the system with the same address as another user.
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