Seth Godin has an interesting post on newsletters ending up in the recipients' spam boxe:
If you send out an email newsletter, you may have experienced the hassle of being blacklisted from an ISP or web service. The asymmetrical nature of spam makes this particularly painful--professional spammers don't mind being blacklisted, because they regularly switch identities. It's the good guys (and the amateur spammers) who get hassled.
Here's a lens that can help good guys navigate their way through the issue.