Many times deals require you to provide a valid email address in order to get them. Once you do that you have a tendency to get a bunch of junk email that you really didn't ask for/want.
To combat this, set up a separate email account for this specific purpose. Get a separate, free email from gmail or yahoo or hotmail and set aside specifically for deals/freebies. This way all of the spam stays there and out of your personal email. I usually keep my yahoo email for all my deals/freebies and I have a separate gmail one for the more important emails because gmail has a better spam filter than yahoo, in my opinion.
You can also do this for survey sites, so that your survey emails don't get lost among your other emails. I usually direct my survey emails to my yahoo account as well.
Making a new email might seem like a lot of effort just for this purpose, but the one time you accidentally delete an important email when you were clearing spam out of your inbox, you'll wish you had taken the 5-10 minutes to make another email address. (Yes, I've done it, and it sucks...a lot.)