I hate it when that happens to me.
Makes me want to write a nasty letter that would surely never, ever be read by anyone at the USPS.
I'd say your dead on with that.Calling them does nothing either.My regular mailman always delivers no later than 10 am,so any later than that,i know it's a substitute.They keep sending the same useless fool every time,he never delivers before 5pm,but usually after 7pm,and not one time have i gotten any mail at all when he works my neighborhood.I found that odd,but didn't think too much of it,until one day,i knew i had a package coming because i checked the tracking that morning and it said it was out for delivery.I watched as he did his rounds,got in his van,and left.An hour later,the tracking said there was no answer at my door,so it was resheduled.A week later the person who sent the package called me and said it was returned to them,with a notice that "The listed address does not exist",i'm pretty sure it exists because i live here haha.I called and complained,was told they had several complaints from people in my neighborhood about him,and that he absolutely would not work our area again.2 days later,same guy,and same problems,in the last year i have had at least 6 packages that never arrived when this guy delivers,i figure he probably throws them away since i complained.Now i ask my regular mailman to give me a heads up if he knows he will be off,so i dont have anything sent during that time.