I have experienced a behaviour that is strange for me and I would be very happy if someone can explain it to me.
We use Zimbra and MS Exchange in split domain scenario where Exchange is the smart host. Zimbra and Exchange are in different geographics locations. Zimbra uses MS Exchange as the Relay MTA, DNS lookups are disabled. Everything was working well until we set up a site-to-site VPN between Zimbra and Exchange locations. There are also DNS forwarders here (Windows AD integrated) that support VPN with providing DNS for corresponding remote location. After the VPN has been set up, I changed Relay MTA setting from FQDN to the external IP address of the Exchange box to be sure that e-mails are not going through VPN tunnel. But Zimbra still tries to relay using the wrong IP address, in fact the internal address of the Exchange box, even after restart of the Zimbra box. This is what I just don't understand to. Why, when there is the explicit IP address entry in Zimbra Relay MTA Zimbra still tries to deliver using another address? Does Zimbra use recursion?
I had to create an explicit host entry in CentOS with the external IP of the Exchange box to workaround this issue.
Using Zimbra 4.0.3 Open Source.