I recently received an email from Sleepycat Software announcing version 4.1 of the Berkeley DB. I'm on their mailing list, so this is completely opt-in, and the content was appropriate for this kind of message.
In the message was the notice:
You've received this email message because your name appears on a list of people who have asked for notification of new releases of Berkeley DB from Sleepycat Software. If you prefer not to receive these announcements, please reply to this message and we'll remove your name from the list. A real human being will read your reply.
Test your mailing list software before a large blast!