Zimbra Collaboration

zimbra admin console

Zimbra Collaboration
(network edition / open source)

> Admin Console

zimbra admin - configure - global settings - mta

Zimbra Administration

> Configure

> Global Settings

> MTA

zimbra admin - mta - relay mta for externa ldelivery

Authentication

Enable authentication [ ]
TLS authenticaton only [ ]

Network

Web mail MTA Hostnames: localhost
Web mail MTA Port: 25

Relay MTA for external delivery: rsxxx.realsender.com : 25
Relay MTA for external delivery (fallback): rsxxx.realsender.com : 25

Please [inform our support team](/we-deliver-your-emails/contacts) that you're using Zimbra Collaboration, so that we configure our servers to accept the connection without any further setup on your side (no need to make any change to the Zimbra's postfix smtp settings)