I received a message from a friend recently asking if I'd sent him a package. I said "no, why?" He said he'd received an email saying there was a package that was stuck and to please confirm. Another friend said he had received a similar message via text. They both have alerts set up.
If you mail a package via USPS or anybody else for that matter or have one enroute then sign up for alerts, how do you know if your message is legit?
If said delivery company does not have your email or phone number you'll know at a glance it's not legit. That's why it's not nessecarily a good idea to sign up for alerts. It's not difficult to check the status via tracking number. And will all of the rampant cyber crime out there, why take that chance?