When I first began couponing I noticed that some of the manufacturers offered their coupons online, via their websites. A few of them required my e-mail address before I could print the coupon. I hesitated, but decided that such reputable companies would only sell my address to other food companies, so any spam I received would be fairly harmless.
Oh, silly, naive me. My spam inbox began to fill and fill. The legitimate companies supplied a link to unsubscribe from their e-mails, but my e-mail had also been sold to x-rated sites wanting to sell sexual enhancement products of every kind. These nasty sites didn't supply a way to unsubscribe.
A year and a half later I still receive 4-6 x-rated e-mails in my spam inbox. And with no way to stop them because they have many tricks to keep you from blocking them. My advice to beginner couponers is to never give out your e-mail address in order to get a coupon, even if it is a big reputable company. I regret that I did every day when I check my mail.