Thanks everyone for the pointers. So the issue is the sympl-ip picks up eth0:1 as the primary and not eth0
However if I use digital ocean Floating IP then it means Sympl binding to the internal address doesn’t matter, as that address is the one the floating ip connects with. So if you are running Sympl on a Do droplet, enable the free floating IP and point your sites at that. The only caveat is that your email server is now a different ip so you need to take that into account when making SPF records etc.
Thanks again everyone
Colin