I am playing with ZCS 8 multiserver installation, and found to be confused with admin GUI settings (Chrome).

Are data displayed/set in Admin GUI kind of template (getting data from some pre-configured values or template), or it should represent actual settings?

Some findings
Global settings > MTA > MTA Trusted Networks
Initial value displays empty field, but postconf command displays initial settings:

$ postconf mynetworks
mynetworks = +{some ipv6 stuff}
If I change this via Admin GUI, restart whole zimbra stack, restart browser (to get rid of cache), still MTA Trusted Networks remain empty in Admin GUI, and postconf gives the same data as above.

Global settings > Proxy > Web Proxy Configuration
According to initial configuration via CLI, I've set Web proxy mode to https, but still Admin GUI preselects http mode, and displays Enable web proxy as unchecked, despite Enabled mode.

Particular settings
I try to implement several Zimbra MTAs in a stack. In ZCS, there are two main settings - Web mail MTA Hostnames (used for mailbox servers to send out mail, composed from Web Client) and Relay MTA for external delivery (mostly used, if you use ISPs or other SMTP servers to route mail outside ZCS user accounts and domains). No actual issues regarding Web mail MTA hostnames, but I initially configured Relay MTA for external delivery, and actually can not understand, whether this setting is compulsory for outside mail routing. I think not, as if mail is composed via Web Client UI, it get's delivered to any of Web mail MTA Hostnames, which are ZCS servers and are able to send mail outside ZCS to other servers.

If both Web mail MTA and Relay MTA are set (different ZCS MTA servers), then mail composed via Web Client gets routed to Web mail MTA (that's correct), and after Web mail MTA reroutes mail to Relay MTA (which would be ok, if it'd be external solution). And again, in this case, modifications made in Admin GUI does not take effect.

This leads to main question - is and in what cases Admin gui is usable at all for main server configuration? It seems, that there is no effect on server settings (user account settings work OK) via Admin GUI. Only CLI and Zimbra commands actually change things in servers. Do you have any other findings on this?