Is there a way to verify mailing addresses are good?

[Benjamin Cowles]

i get a lot of nixies and I thought I'd read somewhere there was a way(website?) to verify they're valid. 

Also while I'm on the subject, a lot of my nixies read "not deliverable as addressed" and I'm taking them verbatim off the local tax assessor website, so does that most likely mean there isn't a person by or close to the name registered with the post office matching who you've addressed your mail to? 

And do any of you know any tricks to determine the error behind this and other clueless "return to sender" messages (i.e. "insufficient address" although g maps and county tax assessor site says otherwise, "attempted, not known" ??)?