Writing in a personal diary or otherwise recording one's thoughts and feelings are examples of

Writing in a personal diary or otherwise recording one's own thoughts is mediated intrapersonal communication.

It is communication with oneself carried through a medium such as a diary.

Mediated interpersonal communication involves another person, who is absent when one writes to oneself.

Mediated mass communication reaches a large audience, not a private diary entry.

Since diary writing fits intrapersonal communication precisely, the claim that no answer fits fails.

Intrapersonal communication is the inner dialogue a person holds within the self.