i was checking out the ow_mailbox_conversation table to see if there was a setting for when the mail message was read and i ran into the word interlocutor.  Althought i know what it means i have never seen anyone use it as a field name in a table before lol.  I am assuming you are referring to the receiver of the message.

I also think we need to add email read to the list of email notifications in the user preferences section. There is a notify for new email but i think Oxwall needs to add the read status as well to that list especially since the data is already there in the DB table.