Enhanced Integration uses IMAP to sync to a user's account directly, it needs the email server's IMAP address (often the same as the SMTP or POP address but not always), the INBOX path, the user's login name, and the user's password. It is very different than Copy & Forward which just sends and SMTP copy of the voicemail.
Enhanced Integration talks directly to the IMAP service of the email server, it doesn't really send messages... Copy&Forward or Forward Only just sends and email attachment. Which one were you trying for, or what are other accounts that work using?