The digest is a forum where Steve fans can discuss the man and his music, and find out about tour dates, television performances, trading, etc. He handles the forwarding of messages in digest format to all persons who request to be on the list. This is done as traffic and his time dictate.
Profanity is a big one, apparently.
There is pretty much always profanity on Exit 0 and if your ISP blocks, you won't ever get a digest. The postal service has nothing to do with it. Only information on Steve's schedule and projects. If you click on the above link, the appropriate subject should be there already. An emphasis will be placed on new dates and changes.