Apparently you want to send emails to the others. That means that you cannot leave the emails unconfigured in CSA.
I normally put my email address as "something" . That is OK in CA PPM and the main result in other systems where I do not want email notifications is that it does not display as a link which opens the email client for anybody who can see that. Non emails from CA PPM of any sort will reach me either. No Spam if I disable email notifications in my account settings.
I cannot think of any adverse consequences.
No consequences that I am aware of. We usually change the email addresses by adding "#" characters to both sides of the "@", in our lower environments so that users don't get emails while we develop/test changes. This also allows us the flexibility to enable emails for certain users when needed.
If you want to disable email notifications for all users, simply change the name of the email server in the CSA to something bogus.
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