It could be either. PayPal does occasionally send out promotional offers, but scammers also send out fake emails offering rewards in an attempt to gather personal information. Always check the email address it's sent from and never click on any links or download any attachments from an email you're unsure about. If you're unsure, you can log into your PayPal account directly (not through the email link) to see if the offer shows up there. If it doesn't, it's likely a scam.