That being said, a proper router with the Hub in modem mode would give you much more control.
@legacy1 Yes thank you I just realised that I can connect with a client redirected to use the new port, but there is no incoming email because port 25 is the default port used by all other servers. So this is not a solution.
It's annoying as I had a hub 1 before and it did allow to forward port 25; hub 3 essentially broke my setup. I seem to have no choice to use the modem mode and another router although I did feel a bit "safer" being behind a second firewall.