We deleted the distribution list and made a new account with the same firstname.lastname@example.org
It is giving errors when we attempt to send to it. The error given from Zimbra Web Client is attached.
I see this error in the /var/log/zimbra.log
Changed domain to domain.com on the above and attachment.
Dec 21 09:21:45 mail postfix/cleanup: 54116270901C: milter-reject: END-OF-MESSAGE from mail.domain.com[192.168.121.41]: 4.7.1 Service unavailable - try again later; from=<email@example.com> to=<firstname.lastname@example.org> proto=ESMTP helo=<mail.domain.com>