You can manage your email preferences either in-app or over the web.
In-app
You can adjust your email preferences in-app by going to Profile > Settings (gear icon) > Notifications > Email.
Web
You can adjust your email preferences on the web by visiting this link while signed into your Untappd account. You can also access this by clicking on the "Unsubscribe" link at the end of Untappd emails pictured below.