According to the DC# on a book I ordered, it was supposedly delivered on March 4th. I have checked the mail every single day and I have not received it. I have a locked mailbox so I know that no one stole it. Any ideas on what I should do?

First, check every place that the mail carrier would leave a package - your mailbox, by the front door, etc. If you still don't find it then check with your post office. Take your tracking number with you and let them know you didn't receive it. They can see who scanned it. And sometimes there's extra information they can see in the scans that doesn't show up for the customer. Also ask them to check their package shelves to see if it is there for some reason.

Did you get a key in the box that day? the package could be in a parcel locker. You would be surprised at how many people don't know what the keys are for, even though they have instructions right on the keyring, so it's always good to ask if someone who has a locking mailbox got a key. 

Sometimes things get delivered to the wrong address.

I also had a package that was scanned as delivered to me that showed up in my mailbox 16 days later.

Ask your mail carrier or at your post office.

We don't have parcel lockers at this apartment complex. I am going to first check with the office to make sure it didn't get left there. I don't think it did since it was a smaller book and definitely would have fit in our mail box just fine. They also call me if I get a package so I don't think they have it. Then, I'll call the post office and see what they say. Hopefully it turns up soon. I waited for a month just to get someone who would send it (I had to let it time out 3 or 4 times before someone actually responded). 

The new scanners the postal service is using has a GPS attached to it. It should show where the carrier was when he scanned your package "delivered". Check with your local P.O.

Ellen, those new scanners are just now starting to be rolled out. Very few offices have the new scanners.