Finding missing email account on a Mac Mail server

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http://serverfault.com – I'm trying to locate an email account, which is auto forwarding to a third party email address, on a Mac Mail server. I have checked Workgroup Manager and check each accounts mail settings but I can't find any account which has the email address or is forwarded to the third party address. I also can't see any 'short' name for the particular email address either. Just wondering if there is another way to trace the source of the email address and then disable the forwarding? (HowTos)