You cannot undo the changes if you mark all messages as read

Original KB number:   290730

Symptoms

If you have many read and unread items in a message folder in Microsoft Outlook, and if you inadvertently select all messages in a folder to be marked as read, there is not an option available that allows you to undo this selection.

Cause

This behavior is by design.

Once you have set the folder and all items in it to be marked or flagged as read, you must manually reset the message items back to their prior status.

Workaround

You can select all of the message items and mark them as read or unread. However, this process is different than returning them to the read or unread status on an individual basis as they were before you marked them all as read.

To work around this behavior, manually reset the message items back to their original status. To do this, use the following methods.

How to mark all folder items as read

1. On the View menu, select Folder List.
2. Right-click the Folder, and then select Mark All as Read.

All of the message items in the selected folder are marked as read.

How to mark individual items as unread

Right-click an item in a folder, and then select Mark as Unread. This returns the individual message item to the unread status.