Email not working after connecting Fortinet forticlient VPN

We are using Fortinet FortiClient VPN for connecting with our company network.

After successfully connecting with FortiClient VPN on iPhone, when we check email it is not working. However, authentication with email server is complete but we are unable to send and receive emails.

Other things accessibility while connecting with FortiClient VPN are working fine.

Help and guidance requested as our iPhone users are badly affected while the same is working smoothly of Android devices.

Note: We experienced this issue after upgrade to new iOS version. Previously, email was working fine while connecting with FortiClient VPN on previous version.

Thanks.