There are several system notifications: on order placement, opening of a new lesson, etc.
You can’t edit its text, but you can turn any of these notifications off. You can create a new mailing with a custom text instead of the system notification.
Here is a list of all notifications ('Messages' - 'Settings' - 'Notifications') and their text:

Order placement, the notification for administrators:

Order placement, the notification for users (you can turn this notification off in offer settings; a list of payment options depends on connected payment systems):

Receipt of payment, the notification for administrators:

Payment acceptance, the notification for administrators:

Response for ticket to technical support team is received:

Response from other user is received:

Comment on a website or a blog:

New comment in a training:

Comment for an answer in a lesson:

Answer to a lesson is received:

Answer in a lesson is checked:

Referral order is paid:

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