Unfortunately, our Updates feature cannot be used to distribute a unique code to each recipient (a la our Send Stored/Generated Codes feature); it can only distribute free download links.
Third-party mailing list services may have a way to distribute codes from a list you'd provide them; we'd recommend checking with Aweber, MailChimp, and GetResponse, as they can also integrate with us to have new buyers subscribed to lists you manage with them (in case you may wish to continue using their services for that purpose). To get a list of previous buyer emails to import for such a mailing list, you can query your E-junkie Transaction Log for the relevant product and date range, click View Log to run the query, then click Download Log to save that log view to a tab-delimited text file you can open and edit in any spreadsheet program like Excel.