You don't. Places that you enter your email address get hacked all the time. Once they have your email address, you are a target. You can't undo their acquisition.
This site keeps track of the various breaches, and will tell you how many sites you have put your email into, that have been compromised.
Last month, a mega compilation of email addresses and some passwords was discovered, so this tends to appear as a recent breach.
If you tend to use the same password all over the place, then there is a chance that the spammers have even got your general password.