GroupWise 2018 upgrade - receiving external emails

Existing GroupWise server: OES 11.3 SLES 11 SP4 GW:14.2.1 Build 125534

New GroupWise server: OES 2018.1 SLES 12.3

DOM and PO data were copied from existing GW to new GW server using rsync.
Installed GW 18.1.1 Build: 125534 including doing the database upgrade to 18.

New GroupWise appears to be operational.
-Can send emails to external.
-Can send/receive internally.
-But cannot receive from external
Gateway firewall (Passthru domain) has been set properly to forward emails to the new GW server.

SMTP logs on gateway firewall says: "error=deferred (connect to[]:25: Connection refused)" is the correct IP for the new GW server.

I've compare settings in GW Administration Consoles but could not find an errors or differences.

It's probably a simple settings error somewhere.

Please suggest things to check.