I found this advice in another forum, where someone had done a similar thing to you and bought a C10 on ebay:
Please follow the steps below in case you have lost your "admin" password on your IronPort appliance.
Contact Customer Support for a temporary password. You will need the Serial Number of the device.
Once you receive the temporary password, please access the IronPort via serial connection.
Log in as user 'adminpassword'.
Enter the temporary password you received from the Customer Support Engineer and hit return.
Enter the new password that will be used for the 'admin' user.
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www.ironport.com/support ··· tal.htmlHope that helps.