You will get informed of Checkin/Checkout Addon via email if you activate their related template and trigger rules.
There is a Default Template known as Admin 4: Checkin/Checkout Addon under Inbox -> Templates:
In order for the email to get sent via email, go to Inbox -> Trigger Rules:
1- The Active status should be Yes. If it’s set as No, click on the pencil next to No to change it to Yes.
Admin 4: Checkin/Checkout Addon 
2- Click on the three dots on the right to Edit.You should click on the Add button to insert the email addresses of Zeevou Users and/or Custom Emails which you want to be informed of Checkin/Checkout Addon. Finally, click Save and Close.
