Disk Doctors product portfolio includes email recovery tools that support both Outlook Express (.dbx) and Microsoft Outlook (.pst). Both the software are capable to recover deleted emails from email archives such as DBX and PST.
Deleted email recovery is similar to the recovery of files from hard drive. All emails are stored in an email archive file with some database arrangements, upon deletion, the corresponding application manages the emails and removes it entries from the table of content. The deleted email still resides in the email archive and gets overwritten upon saving new emails.
Once you are sure that those emails can be recovered, buy the full version of the software to recover those deleted emails.