Connect Outlook Clients Through VPN

Thanks for looking at my question, I really need some help on this one…
We use Exchange Server 5.5 on an NT4.0/6a box. in a Windows 2000 domain.

Remote users can connect to our network through VPN, but cannot connect to the Exchng Srvr.

I’ve routed the following Special Ports assignments on my RRAS server (W2K)to the Exchange Server IP address: 25 SMTP, 110 POP3, 995 Pop3 SSL, 143 IMAP, 993 IMAP4 SSL, 389 LDAP, 636 LDAP SSL, 135 RPC.

Am I missing soemthing? what is it?
Really, thanks for helping me out…
Gerry