I have setup an exchange server in the default iOS mail app on my iPhone X. However, every time I use the FaceID unlocks the screen, all already Email Notifications are cleared so I am unable to see the preview of the messages. The related message previews stay and I need to have the alerts for that. I also have the same problem with my IBM Domino Traveler account, while the iCLoud account works fine.
Email Notifications with Exchange account,Gamil, Outlook always disappear from Lock screen when you unlock the iOS 11 device. This is a bug and it still exists in iOS11.2. It seems that the Face ID are trying to read them and those notifications think that you have saw.
I have faced the same issue with my Microsoft Exchange 2007 on my iPhone X. Finally I get the tips to resolve it.
* Once the FaceID have unlocked the screen, just swipe up from the middle of the screen and then you will find the email notifications are listed there.
* You can also go to re-add your account. Go to the mail settings, delete your Exchange account and add it again. I did that a few times and the Notifications appears. But it seems to stop working after a few hours.
* Open the Settings app from Home screen, tap on Mail, select your account from the list, and then turn off “Show in History” option.
* You could also do that by this way.
Open the Settings app, go to Notifications > Email, and move the switch from On to Off for disabling the feature completely.
Once the Show in History is turned on, the notifications won’t pop up on your Cover Sheet when they come in and your iPhone is locked. But if wipe up from the Cover Sheet or unlock the screen, the full list of notifications are still showing up. The feature may causes the email notifications to be cleared.