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Microsoft Exchange Server database file when gets corrupted then various JET engine errors occur depending on the cause of database file corruption. Most of the JET engine errors can be resolved by executing eseutil.exe, a built-in Exchange Server utility to resolve common MS Exchange Server database related errors. The utility checks the database file for fixing errors. However, some of the JET engine errors cannot be fixed by using the eseutil.exe utility. One of such JET errors is:
-1605 0xFFFFF9BB JET_errKeyDuplicate Illegal duplicate key 4294965691
When the aforementioned error message occurs, you cannot continue working with MS Exchange Server. The specified error message and the situation generally arises when the Eseutil tool recreates B-trees inaccurately. And the Exchange database unable to remount.
This error cannot be fixed by using Eseutil.exe tool. In fact, if you keep trying the Eseutil.exe tool even after getting this error message, it may result in the loss of data and time, and would merely exaggerate the problem. It happens because the /p switch run in Eseutil utility tries to repair all the system tables and indexes. For any table or index which is highly corrupted, the repair is discarded. For such discarded data, ESE Event ID is generated showing bad pages of the data lost during the repair process. This data loss is permanent and would lead to more problems.
Exchange Server experts always recommend creating complete backup of the Exchange Server database files so that when JET errors occur, you can easily recover data. If you have complete backup of the damaged Exchange Server database file then by restoring the backup, you can restart working with Exchange Server without any data loss. But, in case you do not have any backup, you need to take help of third-party Exchange Recovery software.
An EDB Recovery software completely scans the damaged Exchange Server database file (even with Jet Engine errors) and repairs it. After the software completes the scanning process, it saves the recovered data on a user defined location. Kernel for Exchange Server recovery is such a third-party software, which has been designed to provide you a complete Exchange Server database recovery solution. The software supports almost all versions of MS Exchange Server ranging from Exchange Server 5.0 to 2019.
Some Exchange errors like “JET_errKeyDuplicate Illegal duplicate key” cannot be repaired through eseutil utility as it causes loss of data. A powerful EDB recovery tool like Kernel for Exchange Server would be the best option here.