Troubleshooting Exchange 2007 ESE Event 491

My Exchange 2007 SP1 server started reporting Event 491 in the Application Log.

Source: ESE Event ID: 491

edgetransport (3488) Transport Mail Database: An attempt to determine the minimum I/O block size for the volume “D:\” containing “D:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\” failed with system error 5 (0x00000005): “Access is denied. “. The operation will fail with error -1032 (0xfffffbf8).

The Microsoft Exchange Transport service was not automatically starting as well. A few posts I found mentioned excluding the Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue directory from anti-virus scanning. I played around with all sorts of exceptions, but that didn’t resolve my problem. I even disabled the real-time A-V scanner and rebooted the server, but the problems persisted.

After hours of searching I came across this post, which pointed at permissions as the root of the problem. I had removed the default permissions on the Exchange installation drive, and Network Service was missing on the list of permissions. I tried to assign the fewest permissions as possible, but in the end here is what I assigned.

  • NETWORK SERVICE has all rights *except* Full Control and Modify on the TransportRoles folder, and inheritance is turned on. This full path is D:\Program Files\Microsoft\Exchange Server\TransportRoles\ on my server, yours may vary.
  • NETWORK SERVICE has Full Control on the D:\Program Files\Microsoft\Exchange Server\TransportRoles\data\ folder, and inheritance is turned on.
  • NETWORK SERVICE has Read & Execute, List Folder Contents, and Read on the D:\Program Files\Microsoft\Exchange Server\ folder.
  • NETWORK SERVICE has Read & Execute, List Folder Contents, and Read on the root installation folder, which is D:\ for me. I did everything I could to avoid this, but couldn’t make it work without assigning this permission.

After making these changes, reboot your server and you should find Event 491 gone and your Microsoft Exchange Transport service automatically starting once again.