Moving to GCC High: what changes for your staff

Short answer

GCC High is a separate tenant. So everyone who moves gets a new account in a new place. Mail, files and chats arrive by a planned migration, because Microsoft doesn’t support a built-in cross-cloud tenant-to-tenant move (cross-tenant mailbox migration). Phones and laptops are set up again. If it’s planned well, the disruption is small and people know what to expect.

This post is for owners and office managers. It covers what your people will notice and what to tell them before the day. The IT-side plan is in our GCC High migration checklist. The reasons to move, and the work in order, are on the Microsoft 365 GCC High migration page.

If you’re moving only part of the company, only those people change. Everyone else carries on as before. More on that choice in GCC High enclave or full migration, and on which data drives it in what counts as CUI.

Signing in

The new tenant means a new identity. Sign-in for GCC High runs through the US government endpoint, login.microsoftonline.us, not the commercial one (GCC High endpoints, national cloud deployments). Sign-in tokens from the government cloud don’t work with the global service (national cloud deployments). So the old sign-in doesn’t carry over.

It’s a new account, so sign-in methods are set up again. That includes the Microsoft Authenticator app and any phone number used for codes. Tell people this in advance. Otherwise the first prompt to register looks like a phishing attempt.

Old cached sign-ins are a common day-one error. In the OneDrive sync app it shows up as error AADSTS50020. Microsoft says this can be caused by cached identities from the previous tenant, and that it most commonly occurs during a tenant-to-tenant migration. The fix is to remove the cached Office account identities (OneDrive sign-in error). Your help desk should have those steps ready before cutover.

Bookmarks and links

Web addresses move to US government domains. Mail on the web is outlook.office365.us. SharePoint and OneDrive sites are under sharepoint.us. Teams runs on gov.teams.microsoft.us (GCC High endpoints). Bookmarks to the old addresses open the old tenant.

Links inside old emails and documents have the same problem. A SharePoint or Teams link sent last month points at the old tenant. It keeps working only while that tenant stays open. Ask people to re-save favorites in the browser on day one. If a link matters, share it again from the new location.

Outlook on phones

Outlook for iOS and Android works with GCC High without any special configuration (government-cloud Outlook). People install the app, or get it through Intune, and add their new account (government-cloud Outlook).

Some things are different by default, because they don’t meet FedRAMP requirements (government-cloud Outlook):

• Only the work account and its OneDrive can be added on a device. Personal accounts can’t be added.
• Add-ins aren’t available.
• Third-party storage such as Dropbox and Box can’t be added.
• Office Lens scanning, such as business cards, isn’t available.
• People can’t send support tickets from inside the app. They contact your help desk instead.

The first point matters most. Many people keep personal mail in Outlook on their phone. After the move, they can’t. Microsoft suggests another device for personal accounts, or a different mail app (government-cloud Outlook). Tell them before cutover, not after.

An admin can switch some of these features back on. Doing so sends support and diagnostic data outside the government compliance boundary (government-cloud Outlook). We don’t recommend it.

On the desktop, people sign in to Outlook with their new account and a new Outlook profile. Microsoft’s own guidance for tenant-to-tenant mailbox moves says users rebuild their profile with their new sign-in and address, then the mailbox resyncs (cross-tenant mailbox migration). Plan for the same here. It takes a few minutes per person, plus download time for large mailboxes.

OneDrive and files

People sign in to the OneDrive sync app with their new identity. Then their files and folders begin resyncing to the device (cross-tenant OneDrive migration). On a slow connection, a large OneDrive can take a while to come down. Stagger it if the office shares one internet line.

Two OneDrive features aren’t available in GCC High: File cards, and “Shared libraries” in the navigation pane (OneDrive for US Government). People who used Shared libraries to jump to team sites will open those sites from SharePoint or Teams instead.

If someone syncs a library shared by another organization, that may stop working. Microsoft says B2B Sync might not sync files from an organization in a different environment (OneDrive for US Government). For sharing with partners on commercial Microsoft 365, plan guest access carefully so CUI stays on your side of the line.

Laptops and phones in Intune

Intune for GCC High runs in a separate government instance, built on Azure Government (Intune for government). Devices managed in the commercial tenant have to unenroll and then re-enroll in the new tenant. There isn’t a built-in way to migrate them (Intune for government).

Some device features people may know aren’t available in GCC High. Windows Autopilot and Remediations aren’t available, with no current plans (Intune for government). Windows Autopatch, and Windows feature and quality updates in Intune, are planned but not available yet (Intune for government). Autopilot device preparation has some features available now, such as user-driven deployments (Intune for government). So plan device setup around what GCC High offers today, and decide per device type before cutover.

For staff, this is the part that takes real time. Each laptop and each managed phone has to be set up against the new tenant. Book it like an appointment, not a surprise.

Teams

Teams in the new tenant starts fresh. Teams, chats and meeting links live in a tenant, so they have to be set up again in the new one. Microsoft’s tenant-to-tenant guidance says the same about meetings: the meeting link isn’t updated when items move, so meetings have to be removed and created again (cross-tenant mailbox migration).

In practice, each organizer re-sends recurring meetings from the new tenant after they move. Leave the old invites in place until the new ones go out.

Phone calls in Teams work differently in GCC High. Microsoft’s calling plans aren’t offered, so phones run through Direct Routing. Chats with partners in other clouds also change. Both are covered in sharing and Teams after moving to GCC High.

How to prepare people

Most of the disruption comes from surprise, not from the technology.

Brief each wave before it moves. Name the day, and say what each person will re-enter: a new sign-in, sign-in methods in Authenticator, a new Outlook profile on the desktop, and their account in Outlook on the phone. Say which bookmarks change and that old links will stop being useful. Tell anyone with personal mail in Outlook on their phone what to do about it.

Have the help desk ready the morning after. Most questions are the same handful: a cached sign-in error, a missing bookmark, a phone that needs its account re-added. Have short steps for each one ready to send.

Keep the old tenant read-only until checks pass. Confirm every mailbox, site and file arrived before anything is deleted. That keeps a safety net while people settle in.

Talk it through

We plan the people side as part of every migration: who moves in which wave, what they’ll re-enter and what the help desk needs ready. Tell us how many people and devices you have, and we’ll go through it with you on a free 15-minute scoping call.

Book a free scoping call.

We waive the setup fee when you sign up for managed services for 48 months.

Sources. Microsoft facts on this page link to Microsoft Learn. Last checked October 26, 2026.