I have exchange 2000 server and had one of the mailboxes set to forward a copy of every email to another MAPI (user account) account a couple of years ago. I believe initially it was done in Active directory > Delivery options > forward to with Delivery in to both mailbox and forwarding check mark in. I've also tried to setup rules for the mailbox to forward as well.
Since I do not need to forward any emails anymore I've deleted second AD account where emails were forwarded two. I've checked both Delivery option in AD and mailbox rules and do not see any rules which can forward the email yet user in question will get and NDR (for deleted second account) For each email he receives? I can't find the source of the email forwards. Non of the client configuration has any rules either?