Social sharing transactions
It seems to be part of human nature -- the desire to brag about something cool you've purchased or received. You might even be able to recall a time when the idea of being able to talk about owning something was the final factor that pushed you to buy. It happens all the time. Still, as marketers, we often fail to encourage this known behavior through email. This is unfortunate. If your product is cool enough to share, you have valuable brand equity that can be tapped to create raving fans.
One way to spend this brand capital is to incent transactional email social sharing. Transactional emails have an average open rate of 65 percent! You can use this unparalleled visibility and engagement to encourage social sharing behavior.

Take note of how Amazon.com displays social sharing options during the checkout process. Though this is from its website, the same approach can be used in a transactional email by presenting social buttons next to the items in the transaction receipt.
Travel, apparel, and large-ticket items are those things that consumers might want to share. Tech gadgets are also good candidates. Let the consumers judge the "bragging rights" of the purchased item by giving them the opportunity to share with their networks.