I noticed in the ZImbra multi server installation guide, it says that

MTA servers. The MTA server is last because you need to configure one of
the active cluster services’ hostname as the MTA auth host.
If I have 2 active nodes, so only one of them is the MTA auth host right?

Secondly, if I have let say 3 MTA servers eg. mta1.domain.com , mta2.domain.com , mta3.domain.com, how will ZCS use it as a mail transfer agent? When someone send an email.. which MTA server will ZCS use? For receiving of course the mail will be sent to the MX.

Does anything need to be configured? Like the mailbox server pool.. Or should I get it load balanced? I am confused with these.