Device Magic sends various e-mails relating to activity on your account. If you want to opt-out of receiving these mails, you need to edit your user account settings. To do so, login to www.devicemagic.com and locate the personal settings link in the upper right-hand corner:
Now you should see your personal settings. From here you can easily change your password and adjust other preferences.
Decide which communications you no longer want to receive and click "Save settings".
If it's marketing e-mails you no longer wish to receive, you will need to follow the unsubscribe link included therein.