Tracking numbers are the lifeblood of holiday shipping emails. Most emails you'll get from delivery services are tracking numbers. And if you're like some people, including this author, you may check tracking numbers obsessively. 

Hackers know this and send tracking numbers that either aren't legitimate or expired. When a user clicks on that tracking link, it may compel them to engage with the link included. That link, as you might expect, is malicious. 


Any keen observer will notice the sender address is off.