NOTE: It will only work if the email comes from a registered Taskworld email address. Email forwarding is not supported.
See below image for your reference:
If it is the first time you've created a task by email, it will automatically create a Direct Task project in your Project Page List, once a Task by Email has been sent.
Your direct tasks will not be visible to other members unless you make them assignees/followers of your direct tasks
Once you remove the assignees/followers of your direct tasks, they won't be able to open your direct tasks anymore
Your direct tasks will be visible to the members who created them