The original idea was borrowed from this Microsoft blog post , but since not all of the steps were covered there in sufficient detail, I am expanding them here, and adding two specific examples: What is GAL Segmentation GAL segmentation allows one to create an appearance of hosting multiple independent email organizations within the same Office tenant. It was possible to do this in on-prem Exchange , Exchange , and even as far back as Exchange Configure Prerequisites Before we can jump into setting up GAL objects and policies, we need to grant ourselves permissions to manage address lists in Office this permission is not enabled by default.
Also, and this is important , check to make sure that you have either an Enterprise E or an Educational A Office subscription level. Address book policy routing is currently not supported on lower subscription levels and instructions in this article will not work.
Address List Management Roles: To view the current ABP routing setting: To perform the next series of steps, you need to be connected to Exchange Online AND Office tenant for some of the commands, so, continuing from Step 2 above where we connected to Exchange Online, we will go ahead and link up to MSOL service: Connect-MsolService Next we need to get the distinguished name of the distribution list that is replicated from our on-prem Active Directory using Office Dirsync: Next, create a new address list for resource mailboxes: Gal" Finally, we are going to tie these lists together into a single address book policy object: There is a variety of ways to perform this assignment.
The one provided here is by no means the only one or the most elegant one, but it works. First, get the guid of the Office group that was used for address book filtering: Get-MsolGroup Guids will be displayed in the left column. Abp" This command grabs object IDs of all members of our test group, gets their associated mailboxes, and pipes them into commandlet that assigns the new address book policy.
Group get the right GAL automatically. To confirm that your assignment command worked successfully: The approach is the same as above: This next batch of commands requires only Exchange Online powershell session see step 2 above.