junk mail 
noun [mass noun] informal
Unwanted or unsolicited advertising or promotional material received through the post or sent as email: she tossed the junk mail in the bin my inbox is full of junk mail...
- Why is it legal to send junk mail via the post office, but if you send it by email it's suddenly illegal?
- In that world, senders have to pay to send mail: Paper junk mail has to have postage.
- Following an experiment to see just how much junk mail he received in a year, he produced a 70 lb mail mountain.