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http://msmvps.com/blogs/andersonpatricio/archive/2007/06/12/changing-the-queue-database-in-exchange-server-2007.aspx

If you do a default installation of Exchange 2007 the queue database config is located in “C:\Program Files\Microsoft\Exchange Server\Bin\EdgeTransport.exe.config” and the database is stored under “C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\” as default.  To change this settings, we should open the file EdgeTransport.exe.config in this file we have to parameters:

• QueueDatabasePath: Database path (mail.que and trn.chk files)
• QueueDatabaseLoggingPath: transaction logs path (*.log and *.jrs files)

Now, let’s change both parameters for the c:\Database folder, as shown in the figure below. 

Click on the image to see in the original size (readable)

After changing the config file, we have to methods do accomplish our queue database moving process:

Moving the current database

1. Click on Start / Run and type services.msc  click OK
2. Stop the service called Microsoft Exchange Transport
3. Move the database files(mail.que and trn.chk) from original location to the new place
4. Move the transactions log files (*.log and *.jrs) from original location to the new place 
5. Start the Microsoft Exchange Transport service

Creating a new queue database

1. Click on Start / Run and type services.msc  click OK
2. Restart the the Microsoft Exchange Transport service

In both cases the result will be the same, the new database will be changed for the directory specified in the .config file.