USPS has so many problem.
Basically, post office work is delivery but USPS, they lost mail and package a lot. They give tracking number but the tracking system is useless. The system is not updating well.
Secondly, If the mail is missing then customer can't do nothing. When people send email or make phone call to USPS customer service but it is really hard to contact with them. Even if people contact with them, they don't know anything. They only answer is they don't know and just wait.
Thirdly there are no Express mail. I know USPS has express mail service, BUT it is just called express mail. Sometime is late than normal mail and there are no indemnification.
People have dissatisfactions but USPS never fix, the government have to fix.