求救：AP(I-131) 可以用sertified mail寄嗎？

我14日寄出到TSC用sertified mail，今天上網查status如下：
Status: Notice Left

We attempted to deliver your item at 1:18 PM on July 17, 2007 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.

為什麽沒有人簽收呢？是不是不能用sertified mail 寄？如果退回，是不是應該用普通信寄？