epistolary

written in the form of or carried on by letters or correspondence; "an endless sequence of epistolary love affairs"; "the epistolatory novel"

सुमन-कांता उपन्यास में नानक सिंह ने पत्रात्मक ढंग अपनाया है।

Although the epistolary novel style is rare in literary circles it has its own merits.