When corresponding with authors sometimes only the submitting author is emailed, sometimes the principle contact for editorial correspondence, sometimes both. You can also email all authors. One of our journals would like to be able to select the paper’s authors from a list on any email correspondence screen (at the moment they have to copy and paste them from another screen). They would also like to be able to drop and drag email addresses between TO CC and BCC fields (at the moment they have to copy and paste them).
See the discussion here:
Public Knowledge Project Team