Assuming you are taling about OE...you can export the address book..it exports as a 'wab' file. To keep messages..highlight your inbox title, right click and it will give you the path to where all you messages and folders are stored. Alternatively using search, look for 'pst' files and you will find your inbox, outbox, sent items etc mail. Copy these to a seperate location then copy them back once you have re-installed. You can also use the import/export command to copy them in and out of your new app.