I have server with only HTTP/HTTPS/FTP ports open to the Internet. On this I installed ICQ and setup this to work with HTTP port. All worked fine.
After this test, I installed ISA 2004 in Cache mode (one NIC, using another firewall - Checkpoint). All configured OK and working, except ICQ :-(
On client PC is possible to run ICQ, with setting up to connect through HTTP. Login is working well, I see another online/offline contacts, I can add new user and search on server and I can receive messages. But if I try to send message, nothing is comming out (
ICQ promptly show message Faled to send... error number 0314.
With Firewall client is this same, and I think, problem must be on ISA 2004, because on server before installation ISA it worked.