An email from Jon at Dropbox, but when I hover my mouse over his link, it shows a re-direct to muchbloom-1.appspot.com

It's legitimate. It's just tracking if you click on it.

Don't know which email app you're using, but you might be able to view the original email by clicking on the three dots at the top right, and selecting View Original, if the option is there. This will show you the plain text contents of the email without formatting, and sometimes can reveal additional information that might help you determine whether the email is malicious or not.