I can one-up this.
I used to do freelance IT work for an SMB. A manager decided it would be a good idea to to send a charity fund raiser email to their customers (without consulting the boss). The manager did this using the company customer management system. The CMS integrated with Outlook to send the bulk email (1000s of recipients) by putting all the email addresses into the 'to' field. This caused all kinds of trouble.
First of all, the 'to' field was overloaded, so the email was malformed and should have been rejected by 1: The CMS, 2: Outlook, 3: Exchange server, 4: inbound mail servers. The exchange server got stuck in a loop constantly trying to resend a malformed email, with many of the recipients receiving the email multiple times, along with a list of everyone else's email address. Many of the email addresses were out of use or had some kind of automated response, causing a deluge of incoming mail (along side all the customer complaints and malformed email responses). That message was ridiculously hard to exorcise from the Exchange sever - it just would give up.
When the dust settled, there was much groveling to do. This was a data security company, so they lost quite a lot of custom because of this. Needless to say, said manager was out the door shortly after.