I-485郵遞遇到麻煩，請幫助。

本人郵寄I-485到以下地址（delivery confirmation)：
USCIS Texas Service Center
P. O. Box 851804
Mesquite, TX 75185-1804

USPS的Track and Confirm結果如下：
We attempted to deliver your item at 3:26 pm on July 14, 2006 in MESQUITE, TX 75185 and a notice was left. It can be redelivered or picked up at the Post Office. If the item is unclaimed, it will be returned to the sender. Information, if available, is updated every evening. Please check again later.

我的問題
1.下午3:26pm 移民局就沒人收信件了嗎？
2.我是不是不該用delivery confirmation，而隻能用平信。
請過來人幫助，非常感謝！！！