Public host name not routing through VPN on Mobile iOS with Operator APN IPv6

[julien33x]

Hi, We have an Email server that was published online.

We have removed it from online and now available only through VPN.

I have installed OpenVPN Connect and import the ovpn profile on it.
I put the Internal IP of my server on the Public DNS Host.
My Tunnel is splitted.

From mobile (iOS last version 14.4), I have two kind of Internet Mobile provider :
- one still using APN IPv4
- the other one with APN IPv6.

When I connect the VPN from Mobile with APN IPv4 all is ok , all access are working.

When I connect the VPN from Mobile with APN IPv6 :
> Access using Public Host name (xxxx.xxxxx.com) = KO
> Access using Internal Host name (xxxx.xxxxx.lan) = OK
> Access using Internal IP = OK

As a try, I moved VPN to Full Tunnel VPN and all is ok. I would like to avoid getting all Internet traffic on my main internet coonection.

What could I do to keep access only through VPN but not with Full Tunneling ?
Thanks for your help.