Anyone know how Zimbra mailbox servers find the MTA servers to send email? My setup have three mailbox servers and two MTA servers and they are running 7.1. I would like to diversify the email traffic evenly across the MTA servers (now all mailbox servers use the first installed MTA for email delivery), and sometimes one of the IP of the MTA server is blocked by RBL, then I can manually configure the mailbox server to use another MTA server for outgoing email. So, I would like to know how the mailbox servers find the MTA servers to deliver email? And can I do static configuration in the mailbox server to assign primary and secondary MTA servers?