Heads Up: Don't Delete House Party Email

Check your emails from House Party. I got a code for a free Shutterfly photo book. The email gives a code which it says is unique and can only be used once.
The email was from noreply@events.houseparty.com
Here is the text from the email, minus the code:
Something fun, free, and

Something fun, free, and exclusively for you.
Shutterfly, one of our newest partners, just completed 1,500 parties on November 7th. More than 20,000 people gathered to learn about a revolutionary way to make photo books online in minutes, with Shutterfly’s new Simple Path creation process.

What’s a photo book? It’s a professionally bound book featuring your photos on every page. This is the NEW way to preserve and share your memories — making photo books the best holiday gift, ever.

To celebrate their successful party, Shutterfly is offering House Party members the chance to make a free 20-page 7x9 photo book*. The first 10,000 to redeem will receive this $15.99 value. You just pay for the shipping ($4.99 standard U.S. shipping) and the cost for any additionally pages you choose to add.