To allow traffic from a higher security zone to a lower security zone without an ACL on the interface, make sure you do the following.
Create a NAT for the outbound traffic using a static or nat/global pair
ex. nat (inside) 1 192.168.1.0 255.255.255.0
global (outside) 1 interface
ex. static (inside,outside) 1.1.1.1 192.168.1.10
If you have an ACL on the inside interface, you will have to allow the traffic you want to go out in addition to the above.
If you are trying to allow traffic in from a less secure zone to a more secure zone, you must create a static and ACL for the desired comms.
ex. static (inside,outside) 1.1.1.1 192.168.1.10
access-list outside_access_in extended permit tcp any host 1.1.1.1 eq smtp
** Please rate if this helps*
Cheers.
Jay