Yes, it is often possible to retrieve deleted emails - depends on a variety of factors...
If you're using Microsoft Outlook or Outlook Express then you can recover deleted email messages from either your Outlook PST file or Outlook Express DBX files using an email recovery software program.
For example, if its Microsoft Outlook that you use, it should be able to recover deleted email messages and attachments from your Personal Storage File (PST) and/or open and read corrupt Outlook PST files and recover the emails and attachments.
If its Microsoft Outlook Express that you use, it should be able to recover deleted email messages and attachments from your individual Outlook Express DBX files.
For more info visit http://www.repaircorruptfile.com and use the menu on the right hand side for email recovery information.