What does this do when checked? Manual doesn’t really say much. This is the first time I am using NAT on the Mikrotik, and have been having major problems with AIM and VPN’s. I now have AIM running, but had to use the SAME action and check the Not By DST box. It seems to be working now, but I would really like to know what I did and not just click boxes and choices until things work 
Thanks
Mark