This is a strange issue.

Running a Zimbra Network server, version 5.something (the Outlook connector versions associated with this build is 5.0.9.).

The user can email to all of Zimbra's addresses without a problem, but if he tries to email to "", he gets the error:
Message not sent; one or more addresses were not accepted. Rejected addresses: all-kk <>

When I use the admin console to view his mail, I get the same results he does--message does not go through. However, when I use my account, it works fine.

My initial thought was that there may be an error in a Contacts entry that was being mistaken for the "all-kk" list. But this doesn't appear to the case--I'm not able to find any entries that look related. I opened his mailbox and tried sending emails to the distribution list entered in double-quotes, which I assumed would prevent it from "autocompleting."

Has anyone seen this sort of thing before?