A little vague... Did you have another version of OE program on your computer previously?
The only .dbx files that can be extracted from your computer have to be resident on your computer.
If you did not select the option to "Save a copy of messages on server" (OE, Tools, Accounts, Mail tab, Properties, Advanced tab) then there won't be any way to retrieve mail you've downloaded and deleted already in OE.
(If you have access to the same mail acct via a webmail site you might find some of the files)