I sent all my apps & other related docs thro USPS certified mail.
And they reached the schools within 3-5 days.If u r in a hurry, u can try priority mail which is a lot expensive than first class.
Certified mail is supposed to track the package and let u know online the delivery confirmation. Only twice, I could get the tracking information.I could not track Upenn's & San Antonio's but I called up the schools and found out that it had reached them.
Jus to be on the safer side, u can attach a return receipt to ur apps so that if they cannot deliver the package, they will return it to your home address.(Atleast it wont get lost!)