If a user is not receiving emails, the first thing to do is make sure that the user has the correct group assignments. Some emails will send to users based on group assignment, so if the user does not belong to a group that emails were sent to, that user will not receive the email.
Another possible reason emails may not be received is due to the user’s email client or email service. Security settings can sometimes result in legitimate emails being automatically sent to spam or removed entirely. The first thing to check in this case is your spam folder. If mail is being sent to the spam folder or has been deleted, you will need to modify your email settings to allow the emails to come through.