The email reports are created separately for each user and sent to you automatically as soon as another project participant assigns you new responsibilities. These changes are collected and trigger the email report in the morning of the following day.
If you are assigned a particularly large number of new responsibilities in one day, the report lists the latest 20 changes and notifies you of the other changes.
You can easily turn the reports on and off in your user account.
Click on the menu icon at the bottom of the sidebar and then select Account.
At the top right you will find a button to turn the reports on and off.