There are 3 types of epistolar compositions: monological, dialogical, or polylogical ( depending ON whether the work is being carried OUT by 1, 2, 3 (and more) characters ).IN having an interaction between the actors of this narrative, that feedback allows them to have a written comunication. Otherwise....the story told will be more depressing, for being the fruit of a solitary/masoquist act of imagination.

If the connection doesn't even take place between those involved, then what could just be a story of " Pen- friendship " gives way to other of total disillusionment.