Translation:We sent the same letter to all new students.
The English here isn't quite right... it should be "We sent the same letter to all the new students" because it's in the past and so the group of students is specific. The "the" could be left out if the statement is a general one, such as, "We send the same letter to all new students" (every year, for example).
Vor23 brings up a good point. This is a pretty subtle distinction, though, and I imagine few people would appreciate it. Personally, I don't think the main translation needs to be changed to "all THE new students." And both versions should definitely be accepted. Just my opinion, of course! :-)