This article explains how and when it is possible to request a restoration of message archives.

The delete action is permanent. Once a conversation is deleted, it cannot be recovered. For this reason, Yahoo! Messenger asks for a confirmation each time before a conversation is permanently deleted.

If you have noticed that messages are missing from your archive, but you did not delete them, there is a small window of time in which we can attempt to recover the missing messages.

If you have noticed the deletion within the last 24 hours, please fill out the restoration form to initiate a recovery attempt.

The process of restoring your Conversation History or your Yahoo! Mail account will perform a restoration of both your Yahoo! Mail account and your Conversation History. Any messages received after the day and time you selected will not be included in the recovery, including messages received in both Messenger and Yahoo! Mail. For this reason we strongly encourage you to do one of the following for any messages received after that time:

• Forward emails to another email account, such as another Yahoo! Mail account, or Gmail or Hotmail.
• Print emails or instant messages that you want to save.
• Save emails or instant messages to your desktop as a text file.