See pic - this is Beta3:
You should be able to connect any Yahoo! free, plus, or partner account there (with the exception of small business hosting accounts already converted to Zimbra for which you just choose ZCS account type on the main setup page.)
If it's hardcoded @yahoo.com there you're running Beta 2 or prior - then you'd have to use this workaround:
Yahoo! Mail Plus access must use IMAP - but seriously upgrade to Beta 3 in that case.
