все письма были приняты адресатами,

все письма были приняты адресатами, что подтверждено штампами
копия письма с штампами в приложении

Results (English) 1:

all the letters were accepted by the addressees, which is confirmed by the stamps a copy of the letter with the stamps in your application

Results (English) 2:

all the letters have been received by the addressee, as confirmed stamps
copy of the letter with a stamp in the application

Results (English) 3:

All letters have been accepted addressees, die-to-die
confirmed that a copy of the letter from the die-to-die in the annex