After having email notifications turned on for our PPM environment, we are not receiving email notifications from the system. If we change the email address on a resource to a personal gmail account or other, then they do receive the notifications to that account.
CA PPM - SAAS
The problem is on the customer's email server side. The customer's email system is blocking emails coming in from the CA PPM "from" address. The best way to fix this is to engage your email administration team to help find the reason why those emails are being blocked.