Epistolary

epistolary (comparative more epistolary, superlative most epistolary)

Positive
epistolary
Comparative
more epistolary
Superlative
most epistolary
  1. of, or related to letters, or the writing of letters
  2. carried on by written correspondence

An epistolary novel is a novel written as a series of documents. The usual form is letters, although diary entries, newspaper clippings and other documents are sometimes used. Recently, electronic “documents” such as recordings and radio, blogs, and e-mails have also come into use. The word epistolary comes from the Latin word epistola, meaning a letter.

{via wikitionary}