User needs to set up email notifications for time and expense entry approval in Core.

To set up email notifications in Core, follow these steps:

1. Make sure the time and expense entry approvers (or reviewers) are Core users with a valid email and license. 
2. Now log in to Core as an Admin user or Owner.
3. Go to the company menu > Settings > Global Settings > Email Settings to set up all the necessary email information. This allows you to send emails from the program.
4. After saving the information, the Core user who is designated as the reviewer or approver needs to log in.
5. Go to the company menu > User Preferences and under Notifications & Reminders, check all the relevant Reviewer Notifications, such as 'Time or expenses are submitted to me for approval'. 
6. Ensure that the 'Also send notification via email' option is checked. Save your settings.

You can set up other notifications from here as well. Check the Core Help for details.