Need to understand difference between BP and BPP

I am considering Avast Business Protection for 20 workstations and 3 servers.
One server is running Win2003SBS and hosting Exchange.

I already have a robust firewall and all incoming email scanned for spam using outside provider

From what I have read, it seems that only Business Protection (BP) is then needed for workstations (that run Outlook connected to Exchange server) while Business Protection Plus (BPP) is only needed to protect emails on the Exchange server (but minimum purchase of 5 BPP licenses is required).

No one has any other email accounts attached to Outlook - only connection to Exchange.

Is this thinking correct?

Is there any additional licensing needed to ensure Exchange 2003 on the server and Outlook 2003/2007 is protected on the workstations?

Hi,
I understand that you not need Antispam & Firewall, but if you want to use outlook in configuration with your Exchange server I presume you must buy the BPP for all the clients you need.
I think you can’t buy a license of BPP only for the Exchange server, you must buy a number of license equal to number of Pc connected to Exchange server…
I think your local reseller can explain better.
http://www.avast.com/locate-dealer

BPP has extra protection for:
Exchange and Sharepoint on the servers
Firewall and Antispam on the clients

on the website you can see the differences
http://www.avast.com/business