Samsung Email on S10+ only showing unread emails

Samsung Email on S10+ only shows unread emails. I see some (but not all) of the new emails, but as soon as I read them, they disappear. As a result, it always looks like I have no emails, even though there are hundreds of read emails visible on other machines (like a PC using a web browser). I cannot scroll down through previous emails to find a message. Using Microsoft 365 email services and Samsung Email. I cannot find any way to configure this app.