i found that somehow zimbraMTAAuthHost was not set to public name but one of the mailbox server's fqdn instead on a multi-server setup.

from what i can see, if the mailbox were fail to be accessed, authentication won't proceed despite proxied to another mailbox, especially for accounts which resides on that particular mailbox, right?

do i just simply zmprov ms `zmhostname` zimbraMTAAuthHost mail.mydomain.com on all mta servers?