I was recently asked by a journalist, "So who are these spammers, anyway?" There are many different types of spammer. This is one of a series of bulletins describing them.
There are plenty of companies that don't respect unsubscribe requests. This is of course illegal in the U.S. and many other jurisdictions. The club of otherwise-legitimate companies that continue this practice is large, and contains some surprising members.
Sometimes this happens through temporary failure of the back-office list maintenance procedures. However, the legal aspect should be a wake-up call to all organizations that send bulk email to ensure that their unsubscribe processes are working in an accurate and timely fashion.
... Richi Jennings