By default, when you open an email message in your AOL Mail inbox, the email message will no longer appear highlighted. This indicates that you have read the email message. You can, however, change the setting of the specific email message you have previously opened so that the message will appear with bold typeface indicating the message has not been read.
Go to the AOL homepage.
Click the "Mail" icon at the top right corner of the AOL landing page.
Enter your AOL username and email. Click the "Sign In" button.
Select the read message that you want to make unread and bold.
Right-click on the selected email message.
Select the "Mark Unread" option. The email message will automatically bold and appear as unread in the list of your email messages.