I'd like to load balance the zimbraMtaAuthHost setting on my MTAs so that it's not going to a single mail server. I have a VIP created that load balances to my mail servers on port 8443, however I cannot update zimbraMtaAuthHost to a name that isn't a valid mail server. I can change this setting to any one single mail server.

zmprov ms mta1.testdomain.com zimbraMtaAuthHost "mtaauth.testdomain.com"
ERROR: service.INVALID_REQUEST (invalid request: specified zimbraMtaAuthHost does not correspond to a valid service hostname: mtaauth.testdomain.com)

Any suggestions on how to get around this? The entire environment is virtual, so I don't want to go the Linux clustering route. I'd also like this load to be equally load balanced across all mail servers, so I'm looking for more than just HA.

[zimbra@mta1 ~]$ zmcontrol -v
Release 7.1.1_GA_3196.RHEL5_64_20110527001604 RHEL5_64 NETWORK edition.