I have tried the new MAPI on our Bes 4.1.3 and it works perfectly without the exchange management tools installed.
I have introduced a Exchange 2007 server into our organization, moved my mailbox to it, and continued to check BES. Bes picks up the location of my mailbox but cannot open the mailbox...it gets Mapi errors.
I tried ASHWORTH's security settings above and it just does not work at all.
My feeling is that the security being used is from the Exchange 2003 org via the connector and it wont allow BesAdmin to open the mailbox.....
Thats where I am for now...