Recently I got an email in my Unwanted Email box from Hotmail.
I do not check this often, so only noticed this now.
There was an email in it which caught my attention:
USPS Delivery Problem NR5808038
In the mail, there was a file called USPSLabel.zip. The content of the mail was the following:
Only the picture and the attachment were in the email, nothing more, nothing less.
The attachment was already removed by Hotmail as "unknown virus".
USPS or any other Postal Service will not send you an email stating that you need to open an attachment. Certainly do not open the email when you have never used their services before.
If you did order with them and you are in doubt, do not reply on the email but simply navigate to their website (in this case: http://www.usps.com ) and look for contact details.
Additionaly, (correct me if I'm wrong) you can easily compare your tracking number with the one in the subject.