People who run mailing lists, and even some who simply post to Usenet, have had messages bounce back to them with "NDN" in the Subject line. These bounces come from FirstClass BBSes running the PostalUnion UUCP gateway, and usually stem from an incorrect setup. If you are the sysop of a FirstClass board using PostalUnion, you can prevent these bounces, according to Maury Markowitz <email@example.com> of SoftArc, makers of FirstClass. He suggests the following four preventative measures (and if you could send these tips to your FirstClass sysop, those of us who get these bounces will thank you!):
Make sure you have a conference named "JunkNews".
Make sure you have a user or mailing list named "Postmaster".
Make sure you set the expiry dates correctly - one or two days is a good number.
Make sure that you go to EVERY conference that's on the Internet and get Permissions. Make sure that the FIRST line of the WHO field reads "Internet" and "Contributor".