This piece of correspondence is somewhat related to contemporary text message language (also known as txtese, chatspeak, txt, textspeak, lol, txtspk, txtk, texting language, or txt talk).
For example, the first line reads: D r l s, - I in10ded 2 write 2 u b 4, but I had no...
(Dear Les, - I intended to write to you before but I had no...)