I'm not familar with Apple products,
I have a client does security camera installs
he did a home install where they are running Comcast and a Apple Airport for wireless devices, He was trying to get DDNS setup on a security camera DVR so clients can access DVR remotely when away from home. He ended up reseting the Comcast router and the Apple Airport. Now clients cannot access their email accounts when using the WiFi, they have iPhones and iPADs.
I asked them to try using only the 4G cellular and turn off WiFi on their iPhones and iPADs. email works fine with 4G but when they turn WiFi back on it does not work. The WiFi does give them Internet access not email stops working. Sounds like a DNS issue to me. I'm going to stop by later today to try to resolve. I suspect the Comcast router has to be setup again as well as the Airport. Any advice where to start is appricated.