How to Instantly Mark Messages as Read in Outlook 2016 and Prior
One potentially frustrating aspect of Microsoft Outlook 2016 (and earlier versions) is that it doesn't mark a message as read until you've changed your selection. This may not be fast enough for you, but luckily, there's an option to change this setting. Unfortunately, it's buried deep inside of Outlook.
Once you've found this menu, you can also disable the option for navigating messages with the space bar and change how attachments are previewed. Here are our step-by-step instructions for marking messages as read in Outlook.
How to Set Mark as Read Settings in Outlook 2016 and Prior
1. Click File.
2. Click Options.
3. Click Mail.
4. Click Reading Pane under Outlook panes to reveal the Reading Pane options. It's currently set to "Mark item as read when selection changes",
5. Click the box next to "Mark items as read when viewed in the Reading Pane." You can also change the delay timer associated with this option to as low as 0 seconds. Single key reading lets you move from message to message by clicking the space bar. The full-screen reading in portrait orientation option toggles how Word Documents are preview in Outlook.
6. Click OK.
Now messages will be marked as read at the speed of your preference.