Better handling of hostname and email address recommendation.

Like stated [here](https://github.com/mail-in-a-box/mailinabox/pull/149#issuecomment-53111072), if a hostname is box.example.com, we should offer me@example.com as the email address. 

I think this is a better fix than [the previous PR](https://github.com/mail-in-a-box/mailinabox/pull/149).