To enable PST Dumps / Backups on exchange:

1. In the wizard while adding the server select the option for PST backups.
2. On the exchange server itself create a directory in the main drive , call it anything relevant (ie baculapst)
3. Share that folder with windows share functionality with the network

4. Save the job

5. Bacula will now dump and backup PST files for each mailbox in this location