@gwaitsi well, i got to the root of the problem but don't know how to solve.
If I set the GW to WAN1 or WAN2, smtp is working.
If I set the GW to WAN_GW or VPN_FW it is not working.
This is true whether i put the WAN1/2 hard down.
So something with using the gateway group is killing my smtp on certain clients.
Have no clue on how to solve, everything else seems to work.