microsoft outlook

hi everyone,
i just installed ISA server, prior to this, i was using ANALOGX proxy to pop my mails from our mail server which is being hosted by an ISP and configure clients machine using outlook express and microsoft outlook. after this installation of ISA server i installed firewall client on the client machines. they are able to browse the web and clients can pop thier mail using outlook express but clients using microsoft outlook can not pop their mails. is there any setting i have to configure on mirosoft outlook or on ISA client?
pls help me out.