The folks at ExactTarget discovered a few bits of space in E-Commerce land that weren't already supporting advertisements. Such blatant examples of straight communication could not be tolerated. Their target: transactional E-mails.
Here's how they described their plan in a message sent to reporters: "Transactional E-mails, as defined by CAN-SPAM, are those sent after a purchase, confirming a subscription or sharing product update news. In the past, transactional E-mails have been limited to IT systems that used a server to generate an automatic confirmation message. There was no marketing messaging, or up-selling possibilities included in the messages. This was a huge missed opportunity."
Maybe. Or maybe it was intentional, as they didn't want critical confirmation messages to be ignored or deleted. My favorite part is where they bring up the CAN-SPAM Act of 2003—which was intended to prevent unsolicited ads from being sent to consumers—as though it supports this action.