Hi Anna, 

Can you send this into our support team - support@nintex.com.  Please include the email addresses of the users that are not recieving the emails.  Our team can check our email tool to see if the emails are being blocked.  

There is no specific setting for sending the emails when using the checklist tool, however if you are assigning checklist tasks to yourself then no email is sent through, this is because you have assigned the task, therefore you know about the checklist and the task there is no need to send yourself an email.  So when you are testing you will need to test with another user, and assign the tasks to the user.  

The same thing applies for if you check off yours or someone elses activity and your activity is the next one in the list - as you are in the checklist we don't send out an email letting you know the next activity is ready to be checked off, we would only do that where someone else checks off the activity.  

We use checklists for various different things in our own internal site.  We use checklists through our product releases to ensure each step is carried out, or where we need to communicate with clinets regarding their data while investigating support issues.  We use the checklist to ensure each step is followed, and so as the support team we are notified when the dev team no longer need access to that data etc.