You are suddenly best friends with someone, and they want to send you an expensive gift. The gift gets sent by special courier, and you would get an email from the courier requiring payment for the gift. You can give gift card numbers, or better yet – your credit/debit card number. You will not get a gift. The email address is likely from a free email service (like Gmail or Outlook Mail). Sometimes, English is broken, and there are misspellings, and like I said, they would want a gift card to pay for the item.
Red flags are email not from an official company, requiring a gift card, and when you can tell that English is a second language with the person that emailed you. Again, if you provide information that they requested, you will not get the gift. There was never any gift to speak of.