You can send push notifications, emails, or chat messages.
In the admin area, click on Notifications.

Select the desired Communication method from the drop-down menu.

Select your recipient group. It is also possible to define and select individual recipients.

Fill in the fields with your desired message (title / text). You also have the option to include a link that opens when the push notification is clicked.

For chat messages, you can select the sender:

You can limit the list of possible senders. To do so, go to Settings>Chat>Allowed Sender Groups (Administration):

Select the groups to specify the possible senders. Now, people from those groups, as well as you, are available as senders.
Tip: Using a chatbot or dummy user helps keep the chat history organized.
First, enter a subject line. Then use the text box to format your message.

To schedule the message, you can select Shipping time. Click Translations to translate the message into multiple languages. Finally, click Submit.

You can find your message history under 'Sent Messages'.