Responsible for creating the message content.
Responsible for some degree of author and/or content "approval" and
for injecting the content into the Internet Mail service.
Responsible for moving the message from the publisher to Retailer
Responsible for delivering the message to the Reader.
Very broadly, we can choose do aggregate these into Users and Operators.
Users are the producers and consumers of content. Operators do the handling,
to connect Users.
I should have provided a table that links the two sets of terms.
NOTE WELL: This list operates according to