1) Art of epistolary composition 2) Byzantine literature 3) Literary genre 
Epistolography, or the art of writing letters, is a genre of Byzantine literature similar to rhetoric that was popular with the intellectual elite of the Byzantine age. The letter became a popular literary form in the fourth century AD and combined Christian and classical Greek traditions. The collections of the emperors Julian, Libanios, and Syne...
letter-writing
• (n.) The art or practice of writing epistles.
E·pis`to·log'ra·phy noun [ Greek ... epistle + -graphy : confer French épistolographie .] The art or practice of writing epistles. 
epistolography, epistolograph, epistolographic Writing letters (messages).
the practices and principles of letter writing; art of epistolary composition.