Unable to get IP details when firewall switched on.

I am just setting up an old Efficient Networks EN5861 for my home network
but have a problem with the firewall. I have a mailserver on my network
and have setup port forwarding on port 25 for this. I am now building up
an allowed list for the firewall and so far have the following allowed

HTTP outward #For browsing
HTTPS inward & outward #For browsing and webmail on my server
NTP outward #For updating router time
SMTP inward & outward #For sending/receiving mail
DNS outward #For the forwards on my DNS server
BOOTP outward #For DHCP?
TELNET inward #For configuring router remotely (temp)
NNTP outward #For getting my news )

Things work just as I want if I have a connection and then turn on the
firewall. However if I have the firewall on from the start the ADSL
connection shows as STANDBY with the line speed showing. The router does
not receive its WAN IP address and I cannot get connected. At this point
turning off the firewall allows the connection to be made. The connection
is PPPoA if this makes any difference. Can anybody point me in the right
direction. Am I blocking a port I need open for the router to get its IP
address?

thanks

Gav