How to blacklist or reject external mail ids in fetchmail delivery?

We have configured fetchmail to fetch mails from catchall server and delivering to domain.If we send mail to online domain user [email protected] along with local zimbra user [email protected] and [email protected] means online user receiving 3 copies (1 original copy+2 cc copy).How to avoid duplicate mails received from fetchmail in postfix? Below configuration is used poll…