Hi Frado,
When you create a sales order and enter the required date and click on simulate delivery dates button then this basically triggers the Master planning and calculates confirmed ship date.
You also need to remember that if you have many sales orders entered during the day by different sales reps and have a batch run of Master plan then there is a possibility that these confirmed receipt dates will change.
The delays can be observed at Master planning>Common>Requirements>Future messages but if you require email notifications, this will require customization.
Regards,