epistolary style; written correspondence style
Refers to the formal or traditional style used in letters and written correspondence, often contrasted with spoken or modern casual writing.
His letter is written in an epistolary style and is very formal.
A characteristic of the epistolary style is the use of set phrases.
文体 is a general term for 'literary style', whereas 書簡文 is a specific style for letters.
Compound of 書簡 (letter, correspondence) and 文 (writing, style). The exact historical derivation is uncertain, but the term straightforwardly denotes the style of written correspondence.