Skype For Business Trusted Server model

Multiple domains in the Office 365 tenancy can present problems when users try and login to Skype For Business 2015 and their SIP URI is different from the SIP domain.

To resolve this, create a group policy object using the Office 2016 ADMX templates and specifically, the Skype For Business policies contained within.

These are used to add the SIP domain where it differs from the user's SIP sign-in name.

The policy is Computer or User based and will mean that the annoying popup, announcing the SIP domain, sign-in name disparity, is not displayed.

A simple solution, but implementation is very often complicated by the CAB bureaucracy in place within your organisation.