Some email mistakes are worse than others.  Apparently a glitch in a server sent all 4,800 recipients every unsubscribe email sent by members wanting to opt out.  End result: having to delete the entire customer list and starting over.  The sender tried to remedy the situation immediately, but the damage was done.  While some recipients were understanding, others replied with profanity-laced rants.  Morals of the story: check your list, hide your distribution list, make it crystal clear how to unsubscribe, and address a problem immediately.

I would add: do internal testing first, and make sure those in charge of the server know it's working properly.

http://www.dontdrinkthekoolaidblog.com/when-email-goes-bad-a-sad-tale/