We usually recommend new customers to turn on Superfloss and set the aggressiveness setting to Normal. This covers the majority of our customers. If real-time verification isn't needed, or not included in your plan, Autofloss is recommended instead.
We almost never recommend Aggressiveness setting and Superfloss/Autofloss.
Initially, you may want to turn on "Manual Mode" and deal with the invalid email addresses inside of the mailfloss app until you are comfortable with the results and the process.
Once you are comfortable with the process we usually recommend turning on an auto action such as Auto-unsubscribe or Auto-delete. That way mailfloss is entirely hands-off and set and forget.