I was just thinking about this today and google searched to see if this was a feature I was missing out on. I have my personal notes and some notebooks for work meetings. I sometimes email them to the meeting attendess as well.
My problem is that my personal email is associated with the account and after I email the notes, if one of the recipients selects "reply all", now my personal account has these notes - slightly against company policy (separation of work and personal). I can change my email to my work account and back depending on what I'm emailing.
My preference would be
a) store multiple email addresses, designate one as default
the default email address serves as the log in as well as the default across other features
c) where it makes sense (ie emailing notes) allow user to select another email associated to the account when sending those particular notes