If a user is receiving email notifications for a project that they're not actively assigned to — they're likely listed as a project participant in the Resources section.
Participants receive notifications for all project activity until they're manually removed.
Why this happens
A user becomes a project participant when they are:
Added directly to the project's Resources > Resource Allocation table
Assigned to a task within the project
Removing or deleting a task assignment does not remove them as a project participant — they remain in the Resources table until manually removed.
A common example: a user was assigned to a task early in the project, then later reassigned or removed from it. Because participation isn't cleared with the task, they continue receiving notifications even though they no longer have an active role.
How to remove a participant and stop their notifications
Open the project and go to the Resources tab.
Under Resource Allocation, expand the relevant section (e.g., Business, Learning, etc.).
Find the user's name and click the three-dot menu (⋯) next to it.
Select Remove Participant.
The user will no longer receive notifications for that project.