Microsoft offers Centralized Deployment so admins can install Outlook add-ins for many users at once. This is perfect if your company blocks the Office Store globally but needs to allow specific apps (like ExtendSync) for certain users or groups.
Before you start
You’ll need Global Admin or Exchange Admin permissions in Microsoft 365.
Users must be on Exchange Online or a supported Exchange connection (POP/IMAP won’t load add-ins).
Add-ins can take up to 24 hours to appear for all users (often much sooner).
Deploy the ExtendSync Add-in
Step 1: In the admin center of your Microsoft Office 365 account, go to Settings > Integrated apps > Deployed apps > Get Apps.
Step 2: This will take open the App Source page. Search for the ExtendSync app. Hit Next.
Step 3: Choose who gets the add-in:
Everyone – deploy to the entire org, or
Specific users/groups – deploy to selected users or Azure AD groups, or
Just me – good for testing before a wider rollout.
Use the Search box to add users or groups.
Step 5: Click Deploy. You’ll see a green check when deployment completes. Follow the on-screen prompt to test the add-in.
Step 6: When finished, select Next. If you’ve deployed to just yourself, you can select Change who has access to add-in to deploy to more users.
💡 Heads-up: Users might need to relaunch Office to view the add-in icon on the app ribbon. Outlook add-ins can take up to 24 hours to appear on app ribbons.
Reference
If you need more detail, see Microsoft’s docs on Centralized Deployment of Office add-ins in the Microsoft 365 admin center refer to this link.
Tips for Orgs that Block the Office Store
Centralized Deployment lets you keep the Office Store blocked while explicitly allowing approved apps like ExtendSync.
If some users still can’t see the add-in after deployment:
Confirm they’re in the assigned group or user list.
Make sure their mailbox is Exchange Online and their Outlook profile is connected as Exchange/Office 365 (not POP/IMAP).
Have them sign out and back in, then relaunch Outlook.
Check visibility in OWA (Outlook on the web) first.
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