Polite, formal term used in written correspondence to refer to the recipient's letter. Very rare in modern Japanese; mostly found in classical or highly formal letters.
I have read your letter (very formal, archaic).
Formal letter-writing term; 翰 is a classical kanji for 'writing brush' or 'letter'.
Variant spelling using 簡 (simplified, brief); less common than 貴翰.
Compound of 貴 (honorific prefix) and 翰 (classical kanji for 'writing brush' or 'letter'). The exact historical derivation is uncertain, but it follows a pattern of honorific letter-writing terms.