This number is mailbox number for the department.
The voicemail email text when caller leaves voicemail for employee extension does print the extension number. But when the caller leaves voicemail at the department level the mailbox code gets printed which looks odd and does not make sense.
This issue is fixed. The fix now will print the employee name (when caller leaves voicemail on the employee voicemail box) and department name (when caller leaves voicemail on the department voicemail box).
To activate this change into your configuration, you can change any employee name by adding and then removing space, then save the record ( just a dummy save). Wait for 15 mins to take affect.
This will ensure that your configuration will incorporate these changes.