Protocol between outlook and exchange

I`m trying to configure a dial-up networking connection between a client with outlook and a server with Exchange 5.5.
I use a modem connection from the client to connect to my company secure network. I`m able to ping my exchange server and telnet it on port 25, but I`m not able to open my mailbox. Is there any specific protocols or ports that I need to open on the routers or firewalls?

Do I nned to do anything in my Exchange 5.5 (like RAS)? My Exchange 5.5 is connected to my LAN only (no modem).

Will it work the same way with Exchange 2000?

Thanks a lot for your help it`s quite urgent