We are running a single server with GroupWise Mobility Service 2.1, and have a GW 2012 sp2 system with Domains and Post Offices spread over a Wan.
I have been able to add users located on the Post Office specified in GMS as the SOAP server.

The add user fails with users from other POAs in the system.
They can be added if the POA SOAP URL config in GMS is changed to their POA instead, but that breaks existing user mail sync.

When the new user from another POA is added, is sits on SYNCING-INIT for a few minutes followed by FAILED

A Wireshark dump shows the POA containing the user does get the request from GMS via the GroupWise system, but gives out a TCP Reset packet.

I have a test system where all POAs are on the same LAN, running GW2012sp3 and I can add users from all POAs without issues.

There are no firewall restrictions between any of the Domain, POAs or GMS.

Is there any fix for why this is happening?