Just go to USPS.gov and leave some feedback on the local post. I did that once when Amazon.com kicked me an email saying that delivery failed because the postman couldn't get to my house which was odd since I watched the mail man drive up to my house that sunny day. Wasn't any reason they couldn't get to my door with a package.
Called around, unable to locate my actual post because I live in a vortex of confusing addresses. I hit USPS.gov with a message basically stating the above. What I didn't stress, and I realized my error the next day, is that I figured the fault lied somewhere within their computer network and NOT with the driver.
I got a voice mail the next day from the driver asking me, very apologetic-ish, if he'd done anything wrong. I left him a note at the mailbox. It was just the computers that horked up. No big deal.
Basically, I've got a feeling the postal workers take feedback from USPS.gov seriously if they care about their job.
Some don't. I used to drink at a pub that had a postal worker there. Nice guy but a failure at life. Multiple DUI's etc. Didn't have a license and rode around on a bike, usually drunk, and bounced checks at bars.
On the other hand I shoot with a bunch of guys from USPS and they're alright. Almost everybody in the group is former armed services. The one guy that isn't commented the other week that it seems like 80% of the post office is staffed by former military which makes him the odd duck at work. Funny thing, he shoots better than the rest of 'em. Go figure.