Thanks.
I actually read this doc the other day and it only shows how to do the backup via command line.
I need to schedule the job in the Web-based GUI.
I actually got it to work yesterday. The trick was to not user the same string for FTP username and FTP virtual directory name. When they matched, Microsoft FTP acted quite differently and all my backups ended up in the FTPRoot.
So I configured FTP virtual directory name as BRIGHTMAIL01
I created a local user on the FTP server with name brightmail_bak; this is the user name I supply in the Web GUI.
Also in the Web GUI, I supply this for the path:
/BRIGHTMAIL01/