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@田中 寿典
I wasn't able to find anything on changing or adding an email address for notifications. From my experience with Teams, if someone is part of a team they should get emails (unless this feature is turned off), when an action is performed such as chat, meetings, people status, etc.
You can read more here - Manage notifications in Teams
If you have any other questions or require further troubleshooting, please engage our Microsoft Teams forum for additional assistance.
Thank you for your time and patience throughout this issue.