So what happened to the email server?
We had Zimbra version 8.0.2 running on an Ubuntu 10 server. The server needed upgraded to Ubuntu 14, because Ubuntu 10 reaches its End of Life date next month, but 8.0.2 can't run on Ubuntu 14.
The plan was to upgrade the server to U14, then upgrade Zimbra to 8.6.0 for U14. Ubuntu upgraded quickly and without issue. Zimbra's upgrade path is a bit strange, because you basically do a completely new install that then finds your old install and modifies it. Zimbra 8.6.0 failed to start after the upgrade. (It's a frightening process to watch.) Zimbra version 8.0.9 (the latest version of our Zimbra line, which should work on Ubuntu 14) also failed to start, complaining of LDAP issues.
Logically, our next step should have worked: We tried to revert to Zimbra 8.0.2 running on Ubuntu 10, using our backups. Something is not logical about Zimbra, however, and even this failed to start, complaining of LDAP issues. Communications with Zimbra, Inc. have not resulted in any solutions.