What does “This email is an outlier and is excluded from stats” mean?

When your Outlier filter is active, an email with a First Reply Time higher than the number of hours set in the Outlier filter will be excluded from the calculation of your average First Reply Time. 

To turn off your Outliers filter, click on the green tick/checkmark on the right of the Outlier filter. You’ll see your reply time statistics recalculate when you turn the Outlier filter on or off.