Since, the users will interact with RT only through email, I disabled two scrips, On Create Notify Ccs and On Create Notify Other Recipients. This resolved my issue.
But, now the problem is when user will create a ticket through the portal (May be in future), RT won’t send alerts to users in CC on ticket create.
Yes! After enabling $ParseNewMessageForTicketCCs, RT start sending email alerts to all CC emails the support mail itself. Because of this CC users and support email are receiving duplicate emails.
One more thing, after enabling $ParseNewMessageForTicketCCs, RT adds CC users only on new ticket creation not from the followup messages.