What is the weight limit for shipping out of your mail box in the USA? I tried to ship 3 baseballs today and had 6 stamps on each of them and got stickers on them saying anything over 13 oz's has to go to the post office to be shipped. But none of my packages were more than 6-7 oz's... Not to mention a squirrel got into my mail box and ate my envelopes up!!! Not happy today. Thanks!