The email was sent to the email that you have on you Windows Live (Skype/MSN Messenger) account. When you bought it they send you the email.
You probably don't even need the email. Just log into you Windows Live account follow the instructions below:
HP Stream 7 Signature Edition Tablet - Additional Product Information:
To Redeem Windows Store Gift card please visit:
http://www.Microsoft.com/HPStream
$25 Windows Store gift card must be redeemed by December 31, 2015. Customers have 90 days to spend their balance after redeeming the gift card.
Not redeemable on earlier versions of Windows and Windows Phone. Windows 8 users: Update to Windows 8.1 for free through the Windows Store. For full terms and conditions of the offer, visit
http://www.Microsoft.com/HPStream
One year Office 365 Personal subscription included ($69.99 value). Activation required within a limited time.
FREE: Up to 100 Free Skype Minutes - Additional Product Information:
Skype
Thanks for your recent purchase. To show our appreciation, were giving you a complimentary code for up to 100 free minutes of Skype calling.
To redeem your free Skype minutes, follow these easy steps:
Download Skype and register for free at
www.skype.com/voucher.
Follow the online instructions to redeem your code.
Your Skype Credit balance will then update.
Start making calls.
If you have any issues redeeming your free Skype minutes, please contact us. For questions about how to use Skype, see Support Site.