Hope this helps and your problem gets fixed. For instance, are they moving emails to another folder, deleting it directly, or moving it to some other storage location on their own? If a virus-scanner is installed, then you can uninstall this component of the virus scanner so that it doesn’t lead to other issues with send/receive. If you have such add-ins installed, then check their settings to see how they affect emails.
The add-ins usually responsible for this issue are anti-spam filters and virus scanners which integrate with Outlook. Depending on the way they are been used, emails might appear in the Inbox and then be directly removed from it.
There are various scenarios under which you might come across this problem. So let’s see why this happens and what can be done to resolve this issue. Have you ever been through this situation where emails from your Outlook Inbox have disappeared after reading the emails? Quite an annoying situation, right? Well, don’t worry, many Outlook users have been through this.