Interesting discussion about how easy it is to attack someone elses email database to force unsubscribes without the readers permission. With the importance attached to sending out newsletters, this could be serious if your mailing list application is vulnerable Attacking An Email Database
That would definitely not be legal in most places. But that's why I have a third party host my mail apps.
Many 3rd party suppliers seem to be vulnerable as well though. That was the gist of the article. It matters not whom hosts your newsletter, but whether it is vulnerable.