Allow users to specify an email address as public and send only non-sensitive informations to those email addresses (BB-1515)

I am one of the developers of PyPy: our main repo is owned by the "pypy" user, which is of course not a real person. At the moment, the email address associated with it is mine, and thus I am the only one to get notifications such as forks and pull requests.

I wanted to set the address of the mailing list as "primary address", in a way that everyone can get the notifications. However, this is not possible because else people could just use the "reset password" button to send a public message to the mailing list.

It would be nice to mark a specific email address as "public", so that only non sensitive informations are sent to it.