Click 
Mailbox in the Folder List.
Select the item, then click Read Later at the top of the Item List.
or
Click the item to open it, then click Read Later.
Click Mailbox in the Folder List.
Select the item, then click Read Later at the top of the Item List.
or
Click the item to open it, then click Read Later.
Note: Using Read Later does not change the status of the item in Properties. For example, if you have opened an item, then marked the item unread, the sender of the item still sees the item status as Opened in Properties.
Related Topics
To check the status of an item