Windows – Prevent Outlook 2016 from closing when minimized

Make sure you have no unread messages in your mail. Send yourself an email. The icon should appear. BEFORE it disappears right click your taskbar > Properties and "Customize.." and you will see a new Icon there that is not in the list if you try this without having the unread mail icon showing.

It is called Microsoft Outlook and underneath says You have new unread e-mail messages. Change the behavior of this from "only show notifications" to "show icon and notifications"

Now it should stay. What a horrible way to do this.

The only option I know could control the meeting invitation deletion behavior is what you have mentioned: Delete meeting requests and notifications from Inbox after responding. According on my testing, when this option is unchecked, the meeting invitation should be deleted after responding. Maybe you can try creating a new Outlook mail profile and set up your email account in the new profile, and then see whether this issue continues.

Besides, if possible, try set up the email account on another computer and see whether the issue follows the account.