When you create an announcement, when you are ready to publish it there is a setting that if selected, the announcement is emailed to employees.
If this option hasn't been selected before you click Publish, no email is sent to your selected audience. This is usually when employees don't receive an email notification.
This option disappears once the announcement has been published, so you can't edit the announcement to select this setting.
How do I email this announcement after it's been published?
If you want to email this announcement, you must create the announcement again, and make sure to select Send selected employees an email notification about this announcement.
Once selected click Publish.