ISA Server and Outlook

Hi everyone,
last week i installed and configure ISA Server on our network in integrated mode.Clients can now browse internet using Web Proxy on ISA Server.But problem is how can i configured outlook express or any mail client to use ISA Server.Our mail server is provided by our ISP,we dont have local mail server.(Our mail servers is let say, pop.mydomain.com and smtp.mydomain.com)

I already configure Packet filter to open POP3 110 incoming and SMTP 25 outgoing.How can i setup or configure my mail client to use this?

Thanks and hope for a response…