I'm feeling guilty for not having posted regularly much lately, so just going through an archive of useful little tidbits I've archived over the years, I ran across this one:
Q: What is the name of the attribute that controls whether or not a public folder is mail-enabled?
A: Set PR_PF_PROXY_REQUIRED to true, and PR_PUBLISH_IN_ADDRESS_BOOK to true to - you'll never guess on your own - show the entry in the address book.
The process of getting the proxy object created and subsequently assigned an email address is a very asynchronous process, don't expect delivery to the public folder to work immediately after setting these props.
 I have two kids and a full time job. Nuff said. I stole this sentence verbatim from an awesome dev.