请问一下，如果用网申，推荐信能空吗，我想让推荐人写信然后寄过去，可是担心这样网上的package 不全，这样不能成功。有谁知道吗？

Usually you can select "submit rec letter offline" in schools' online application system. Try to find it somewhere.

depends on the online system. for some, you can leave that part blank, others you cannot.
in fact, most online systems provide two options about the recommendation. but at least the Georgia tech cannot.
that is my experience.