все письма были приняты адресатами,

все письма были приняты адресатами, проставив подтверждающие печати на копии

Results (English) 1:

all the letters were accepted by the addressees, including supporting printing on copies

Results (English) 2:

all the letters have been received by the addressee by putting confirming print copies

Results (English) 3:

All letters have been taken by addressees, including accents print proof in the copy