There are a few ways in which you can receive notifications from Mingle.
1. If you are tagged/mentioned in a murmur, you will receive an email with the message and an option to reply directly from email.
2. You can subscribe to pages and/or cards to be notified immediately when a change is made to a card/page that you're interested in.
You can also manage your card/page subscriptions in your profile page under the Subscriptions tab.