Within Teamwork.com, you can choose to notify assigned users of task changes.
When you make a change to an existing task you can choose to notify people via email of these changes.
Note: If the task is assigned to you only, you will get an email notification. If the task is assigned to multiple people including you, you won't get notified but the other people will.
When editing a task, check the Notify by Email option below the assignee field in the Task details tab.
The email will include the task name, a link directly to the task in your Teamwork.com site, and the user making the changes.
You will also see a list of the task properties changed by the user.
A summary of the task's updated properties will be listed at the end of the email.
For more information, see: Interacting with Tasks via Email