I added my Outlook 365 business email account to my Galaxy S7 phone when I bought it 2 months ago and I have been plagued by my email being shown as read on my desktop Outlook at work since. I am missing emails because they are marked as read, and they are not. This did not happen before I added the account to my phone. I rarely even open my email on my phone for work, so why is it marking them all as read?
This is happening because your phone is setup to use POP3 and the POP server is marking emails read after downloading them on your Galaxy S7 Android. You can set up Exchange on your phone to have an exact copy of the mailbox on each device or you need to manually mark the emails as unread which is not a very practical thing to do.