Email message: “Network settings prevent content from loading privately”. How do I fix this?

I’m getting the above message at the top of every email on a new iPad Air so I took it into an Apple store. The techie didn’t seem to know anything about it—and it didn’t happen in the store when I opened my emails. He checked my network settings and found nothing wrong, so he suggested I call my service provider (Verizon). When I got home, it started again. Still getting the above message on all emails. Why? Why only at home? How do I fix it?