I am using the latest version Boxzilla and MailChimp for WP
Boxzilla – Version 3.1.4
MailChimp for WP – Version 4.0.3
Here is the screenshot showing the other message if the email is invalid.
View post on imgur.com
I am expecting the same result for the success message but it is just going back to the subscribe window without the ‘Successfully subscribed’ message.