Our firm recently merged, bringing together 300 employees from our side and 130 from the other. Both companies use M365, and each is adamant that their setup is the best to keep. This has resulted in two Global Address Lists (GALs) and separate directory structures, making it difficult for anyone to find contacts from the other company without contacting IT. Our clients are even noticing that their usual contacts are missing from the directory. I anticipate that a complete tenant merger will take at least 6 months because of compliance teams and data mapping, so I'm wondering if there's a way to sync our two M365 tenants into a single address book without undergoing full migration. The ideal solution would also ensure that both directories are available on mobile devices since our team prefers calling over checking Outlook, and it should prevent users from making unwanted changes to the GAL.
4 Answers
Definitely look into MTO! I set it up recently and found it surprisingly straightforward. You can even differentiate users by appending to their display names in the GAL if needed. While users will still operate within their respective Teams tenants, MTO makes chats simpler as it removes external tags. This provides an immediate relief from the 'can't find anyone' complaints.
It sounds like you're dealing with a classic multi-tenant situation. Utilizing Multi-Tenant Organization (MTO) could help you bridge that gap quickly. If you need a short-term fix, MTO could allow for contact visibility without having to wait for a full migration. Just be aware that this setup won't integrate contacts directly into mobile address books—it's focused on connecting Outlook and Teams.
There’s an easier way to solve the GAL issue without full migration. Just create external contact cards for users from the other tenant. It involves some exporting and scripting, but it’s a temporary solution that you can implement quickly. Keep in mind that while it addresses the GAL problem now, you'll have some cleanup to do when merging tenants later.
You could also consider creating a third tenant and moving everyone over. This could simplify things by leaving behind unwanted customizations. As a quick fix, you might add each other's GALs as contacts and enable free/busy sharing on calendars, which shouldn’t be too labor-intensive.
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