In the 18century the Epistulary novel arrived in Europe because long letters were considerated important for the comunication.
The first international succes is "Lettres persones",a philosophical novel by Montesquieu.
The epistolary novel shows in fact a variety of contents:

-novel based on unhappy love like Goethe and Foscolo's novel
-novel whit strong social tones like novel by Richardson

Epistolary fiction is a popular genre where the narrative is told via a series of documents. You have almost certainly read one of these books. Letters are the most common basis for epistolary novels but diary entries are also popular. The word epistolary comes from Latin where epistola means a letter.

In the days before emails and text messages, letters were an essential part of everyday life and it was only natural for authors to embrace this form of communication.

 Samuel Richardson wrote two successful epistolary novels – Pamela in 1740 and Clarissa in 1749. Johann Wolfgang von Goethe’s The Sorrows of Young Werther was another important example in 1774. The History of Emily Montague (1769) by Frances Brooke is another 18th century novel of this type. Epistolary fiction become so widespread that Henry Fielding parodied Pamela with a novel called Shamela in 1741.

Some authors use correspondence or documents for the entire text while others, like Herzog by Saul Bellow and Super Sad True Love Story by Gary Shteyngart, use them for particular sections.

Bram Stoker’s Dracula is perhaps the most successful novel of all time to be written in this format but others include Stephen King’s first published novel, Carrie, Alice Walker’s The Color Purple and Bridget Jones’ Diary.

Tecniques

The epistolary novel presents a great tecnical variety.We may distinguish between "a single-point-of-view" epistolary novel or "a composite-point-of-view" epistolary novel.(difference is in a one or more correspondents)
Also importanto is the role of EDITOR who pretends to have found the letters and presents them to the pubblic.
 

Richardson's revolution

Samuel Richardson(1689-1761) was the first writer who drammatize letter-writing.He uses many devices for making his letters lively and intensly dramatic,as if they were written to the moment.Such is the dramatic, or melodramatic power of Richarson's novels that letters in them seem to have a life of their own:they are interrupted,idden,lost,found,stolen,given back,counterfeited.

Society in Epistolary novel

The epistolary novel served a dual purpose:
-On the one hand, writer found in letters the ideal for giving their view of man and society
-On the other hand, became the means of psichological analysis of characters.