I hope this is enough information to answer these questions:
Say I have a a mail server on the inside interface(10.1.10.1) and it is required to relay to a server on the DMZ interface (192.168.1.1).
With the below config parameters is the following tru:
1. The inside Network is going to nat anything to from the inside network to the 192.168.1.254 address.
2. Everything inbound to the DMZ server from the Inside interface will look like it is coming from the 192.168.1.254 address.
3. All traffic originating from the DMZ server will send to the 192.168.1.254 address.
4. the access list DMZ is not needed in this case to allow traffic to host 10.1.10.1
global (DMZ) 1 192.168.1.254
nat (inside) 0 access-list NO_NAT
nat (inside) 1 0.0.0.0 0.0.0.0 0 0
access-list dmz permit tcp host 192.168.1.1 host 10.1.10.1
access-list dmz permit udp host 192.168.1.1 host 10.1.10.1
access-list NO_NAT permit ip host 10.1.10.1 host 192.168.1.1
access-list inside permit tcp host 10.1.10.1 host 192.168.1.1 eq smtp