The U.S. Postal Service warns you to ignore emails that say they have a package for you, but the longer you let it sit at the post office, the more it's going to cost you.
Some of the emails claim the USPS will charge you $20 for each day the post office has to hold it for you. If you have a package the post office needs to deliver, they're not going to email, nor will they charge you to hold it.
You should delete the email and make sure you don't click on any links that are in the email.