You can control this in just two ways: (1) For a specific project, for a specific user. (2) For all projects, for all users.

FOR A SPECIFIC PROJECT:

1. From the Project, click the EDIT from within the Manage (3 dot) Menu:

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2. Find the Project Manager in the list of Followers and Edit their subscription:

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3. Choose what they will follow:

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FOR ALL PROJECTS:

1. Activate Developer Mode.  Navigate to Settings --> Technical --> Email --> Subtypes.

2. Filter for the Project model:

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3. Open and Edit the DEFAULT boolean on each as needed:

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4. Filter again for "Model is not Set" if you want to change the defaults on ALL Models (not just Projects):

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Consider that Projects can be DUPLICATED (from the same EDIT menu - after saving - access Duplicate from the Action Menu) , and you can therefore use Projects as 'templates' for other Projects.