I believe your preferred dns server should be set to google 8.8.8.8 not your router ip address.
In CERTAIN cases like VERIZON FIOS routers you will use your routers address as PRIMARY and SECONDARY...not google's.
If email tests are NOT working for some Hikvision cameras using gmail..use port 465.
AND there are a lot of quirky things going on with VERIZONs Port forwarding.
If you have multiple cameras...We started HTTP Port on camera 1 as port 81..and increased each camera incrementally by one port number.
Same with RTSP (554,555,556 etc) ,
HTTPS (443,444,445 etc.) and
Server port....(8091, 8092, 8093 etc)
NO PORT NUMBER should NEVER be the same among multiple cameras (If you are using VERIZON Fios routers - could be the same issue for others I dont know..but I've spent days on this issue) INDIVIDUAL and separate sequential port numbers for each camera SOLVES a lot of issues like the stream doesn't show up or you have the same stream image coming in from what appears to be a different camera.
There is a port number in the high 80s...87 (I think) that CANNOT be used so you might have to skip if you have more than six cameras.