Updated Sept 1st 2011 - To recover a deleted facebook email message, find the undo link (located in yellow box) below the + Compose link.
If undo doesn't work then we recommend Data Recovery Pro which has built-in email recovery features. In fact, this tool has a free scanner so that you can see if your Facebook emails are recoverable before you invest any money in the product.
Recovering Facebook Emails
When Facebook sends emails to you, it sends them to the email address that you have on file with Facebook and according to the settings you have specified. Recovering the Facebook emails will depend on how you received them in the first place. For example, do your Facebook email messages arrive in Microsoft Outlook, Outlook Express or Windows Live Mail or do you check your email account online such as via Gmail?
Email Recovery Steps
The first step for both email software and Web-based email is to check your Deleted Messages or Deleted Items folder. If you deleted the messages but have not yet emptied your Deleted Messages folder, the messages will be waiting for you. Simply click the folder and browse through the list in search of the missing Facebook emails. Another option is to use your email program's search box to search all folders for messages from Facebook.
Email Recovery Software
Now, what if you emptied the Deleted Messages folder? If you emptied a Web-based folder, then you are out of luck unless you downloaded the messages to your computer. On the other hand, if you opened the messages from either Outlook, Outlook Express, or Windows Live Mail, you do have options! Email recovery software exists for recovering deleted messages. You need to be careful to select a data recovery program that has specific capabilities for recovering email messages for your specific email application.
Recover Deleted Facebook Messages
Here's another situation: What if you deleted a message on Facebook and want to recover it? If you have the original email notification that Facebook sent you, open that notification and scroll down to the section that says, "To reply to this message, follow the link below" and then click the link. Since the message has been deleted, you won't see it; however, a new link will be provided labeled, "Show deleted thread." Click the link and view the deleted message.