Hey there,
Thanks for posting. The plugin utilizes MailChimp’s double opt-in process, which means that before an email address is added to the list, the subscriber themselves will need to click on the opt-in confirmation link that’s present in the confirmation email in order to be added to the list.
Can you elaborate a bit on your concerns of knowing if it went through? Are you specifically concerned about the email going through, or the subscriber being added to your MailChimp list successfully?
For the “thank you for your subscription” message, that’s something that would be set in your MailChimp account, using your list’s form builder. This kb article should get started, and if you have any additional questions, that’s something that would be best handled by MailChimp’s support team, which can be reached through any of the links on the right-hand side of that kb article:
How can I create and customize signup forms and response emails for my list?: https://eepurl.com/gOGZ