To segregate companies in Lync we would use the msRTCSIP-GroupingID attribute on the user Object.
Default value for this attibute is “<not set>”
This would as expected result in the default addresslist 00000…….
If we add a value to the attribute i.e : 00 11 22 33 44 55 66 77 88 99 AA BB CC DD EE FF
After adding this new value I would normally run :> update-csaddresslist
We now get a new a addresslist based on the msRTCSIP-GroupingID value.
This will be the addresslist users searches from Lync.