"you can keep this letter or trash it" suggests to me the possibility of the letter being intended to be internal. One employee informing another that the card in question was mis-spelled, so that they could figure out what the writer was discussing. That is the lone place there is a "correction". The other highlighted parts seem to point out his tone and the last, what method would have been preferred.
2008 Topps Chrome Red Refractor SET #'d/25 98.8% complete!
NEED THESE 4 - PLEASE LMK!!!
55 Orlando Hudson,150 Homer Bailey,191 Edinson Volquez, MHRC536 Mantle HR #536