We are using EAS and Outlook 2016.  We have one employee that is having an issue in both Outlook and on his iPhone.  If he opens and email when he goes and opens another one the one he just had opened disappears.  If he logs into the web client all the emails are there.  I've deleted his account and re-added it and it worked fine for day but the next day it started doing it again.  I've checked all the settings in Smartermail and his account is the same as everyone else.