Environment: NW65sp2+BM38sp2a (Firewall) NW65sp2+GW652(Mail server)

Static NAT is used so that the mail server can receive mail from outside.
The mail server binds with IP addr X.Y.0.21, and the Firewall binds with
a 2nd IP addr A.B.60.243, which is NATed to the mail server's addr.

Dynamic NAT is also enabled on the Firewall

I have setup a stateful filter for ICMP so that all internal machines can
ping outside. I notice that, with static NAT enabled, the mail server
can't ping outside; when static NAT is disabled, the mail server can ping
outside.

The NAT seems to be the culprit in my case. How should I set the filter
in such scenario so that the mail server can ping outside using ping-st,
while preserving the static NAT so that the mail server can receive mail?

Jimmy