One constant frustration for railway museums is wrong addresses.

Well I just "accidentally" found a way to have mailing lists thoroughly checked for errors -- for free.

http://www.click2mail.com/ is a service that takes your word doc, your mailing list, and bulk mails it. But first, they thoroughly clean your mailing list. Their goal is to figure out which addresses are "machinable", qualifying for 38 cents instead of 44 cents postage. You have to sign up, but not use a credit card before you get this far.

The side effect is that you land at a screen which lists all your "broken" email addresses.

I ran a list of about 330, and I hit 27 "bad" ones. Some of them were trivial, such as "125 A Walden Pond" instead of "125 Walden Pond #A". But some were serious - like 1234 Joseph Lane instead of 1238 Joseph Lane.

Now mind you, Click2Mail doesn't correct your list, only flag them as wrong. I used several other resources to correct them.
The Post Office zipcode calculator helps validate. http://zip4.usps.com/zip4/welcome.jsp
http://www.whitepages.com/ helps me look up people whose name and state I know.
Also http://www.anywho.com/
And Google/Yahoo search let me search for the person's name and/or their address. So I might type the name of a street and city without the address # and see if there's anything funny there.

Anyway I was able to "clean" all of them without too much work.

Non-profit organizations can register with click2mail.com and receive even lower postage rates.