expression
Archaic expression used in formal letters to convey hearsay or reported information. Equivalent to modern 〜だそうだ or 〜とのことだ.
「御無事にて御渡海候由、珍重に存じ候」のように、手紙文で使われた。
It was used in letters, as in 'I hear that you crossed the sea safely, which I find most gratifying.'