I cannot connect directly to the camera unless I connect to one of the Ethernet ports on the NVR, or by connecting to the camera via the NVR IP, and a port number such as 65004
Yes, so the converse is that the NVR PoE-connected cameras cannot connect to the LAN, or to the internet to send email.
On a Hikvision NVR - and yours may be a Hikvision OEM model, though it may have less functional firmware, this is needed to allow such cameras to access the outside world - 3 requirements to make this happen :
In this example, I'm assuming the Hikvision default NVR PoE interface ('Internal NIC' in the VGA/HDMI interface) IP address is 192.168.254.1 Adjust yours to suit.
Enable the NVR 'Virtual Host', which you probably already have done.
Change the channel mode from Plug&Play to Manual, to prevent the NVR from re-configuring the camera network settings, then access the camera web GUI via Virtual Host and change the camera default gateway IP address to 192.168.254.1 It's likely to be initially set the same as the NVR default gateway.
In your LAN router/gateway, add a static route along the lines of :
"For network 192.168.254.0/24 (ie subnet mask 255.255.255.0) use <IP_address_of_NVR_LAN_interface> as the gateway"
Test the result by :
ping <camera_actual_IP_address>
If that's OK, access <camera_actual_IP_address> with the PC browser.
Then use the Test button in the camera web GUI to check the ability to send email, or to access an NTP server.
This assumes the camera DNS settings are valid, usually your LAN router/Gateway.