Synonyms:
epistolary, epistolatory
Meaning: written in the form of or carried on by letters or correspondence; "an endless sequence of epistolary love affairs"; "the epistolatory novel"
Usage examples
Sorry indeed were these days for Billy; and, as if to make her cup of woe full to overflowing, there were Sister Kate's epistolary "I told you so," and Aunt Hannah's ever recurring lament: "If only, Billy, you were a practical housekeeper yourself, they wouldn't impose on you so!"