Email API v.2 - From Object Explained

from Object is of type emailAddress, but it holds a special functionality.
When you have configured your Domain(s) and added authorized senders, you have invited a number of persons / email addresses to act as content generators on your behalf.

from An Object indicating who will appear as sender in the message.

nameStringThe friendly name of the sender
addressString (email address)The actual email address of the sender.
Must be a well-formed email address. Must not be blank

As with to and cc emailAddress items, from will also be visible to all recipients of the message.