It's quite strange because it's not as though I'm not receiving any mail - but so far quite a few have gone missing, and I almost missed paying my Rueckmeldung because the form didn't arrive. So far I have missed several letters from banks and other such things. In total I would say I only receive about 75% of my mail - or possibly less, because I'm sure there's more mail I've missed that I just never found out about for whatever reason.
Could it just be a lazy postman? It also happens frequently that we get notices saying that we must pick up our packages because we weren't home to receive them...when in fact we were home all day.
I feel quite annoyed that German stereotypes of efficiency and punctuality don't apply to things that are actually useful!