Want to be a Permanent Resident? - Part II

Here's what the tracking status on USPS says on the delivery status of my package :

Status: Notice Left

We attempted to deliver your item at 10:57 AM on May 8, 2007 in MESQUITE, TX 75185 and a notice was left. A second delivery attempt will be made. If unsuccessful, we will hold it for five business days and then it will be returned to the sender. Information, if available, is updated every evening. Please check again later.

Wha????
I had to mail it to a P.O Box address for crying out loud. Ofcourse there won't be any person on hand to accept that mail. What on earth are they talking about ??

Update :

Status: Delivered

Your item was delivered at 5:32 AM on May 9, 2007 in MESQUITE, TX 75185 to INS . The item was signed for by M S.

So are they saying someone actually works at the INS at 5.32AM ? But I mailed it to a P.O Box Address so how is it possible that someone actually signed for it ?
Errr... I don't get it.
Nevermind. I just hope it is in good hands.