Block Blackberry access to qmail mail server
 

Is there a way to block Blackberry's access to qmail mail server? It is against my company policies to store password with 3rd party (BIS)..

Blackberry's access to qmail mail server should base on username... for example all top management people should be able to connect to qmail server using BB but for others it should be blocked.

Blocking the BIS IP address range will not work in this case.

(qmail is linux based mail server)

any help?