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USPS offers tracking ($1.60 extra, Form 152) for Priority Mail, First Class Parcel and, Package Services Parcels. They will email you with the status - see "Track and Confirm" on the USPS.com web site.
Form 152 is just delivery confirmation. It is not tracking and can take days after delivery for any information to show up on the web site. Delivery confirmation is no longer available on first class letters.
"Some items cannot be sent with Delivery Confirmation of any kind. These items include letters and flat pieces sent by First-Class Mail and Package Services".
"Enter your label number to see the status of your item. If you shipped with Express Mail®, you’ll get point-by-point tracking details. If you used another service—Delivery Confirmation™, Certified Mail™, Registered Mail™ —you’ll see when it went out for delivery"
USPS does not offer tracking of any sort except on Domestic over night Express although they will tell you they offer it on International Express but it usually stops tracking once the parcel leaves the US.