Shared Email Marked As Read

My wife and I got the iPhone 7, and are having problems with email. For years we've had iPhone and shared the same email address. An email would come through on both our phones and have the blue dot. If either of us was to read the email, the others would remain in the inbox with the blue dot, unread. Even though the other had read it.

At the moment we are getting emails and missing them because they are either arriving in the in box with no blue dot, not read anywhere. Or when one of us reads them, the other misses them.

I vaguely remember there being a way to stop this as I've had it before, but for the life of me I can't find the answer or the setting.

Any ideas?