Outlook Mobile Government Cloud (GCC): How to Sign In to GCC-High Tenant

Outlook Mobile for iOS and Android supports Government Community Cloud High (GCC-High) tenants, which are separate from commercial Microsoft 365 environments. Many government contractors and agencies use GCC-High to meet stricter compliance and security requirements. Without the correct configuration steps, users see sign-in errors or cannot find their mailbox. This article explains how to sign in to a GCC-High tenant on Outlook Mobile and what settings must be in place.

What Is GCC-High and Why It Requires Special Sign-In Steps

Government Community Cloud High is a physically isolated instance of Microsoft 365 built for US government agencies and contractors handling Controlled Unclassified Information and ITAR data. GCC-High uses different domain endpoints than commercial Microsoft 365. The Exchange Online endpoint for GCC-High is outlook.office365.us instead of outlook.office365.com. Azure AD authentication for GCC-High also uses a separate login page. Outlook Mobile cannot automatically detect a GCC-High tenant using standard autodiscover because the DNS records point to the commercial cloud. You must manually configure the account settings on the mobile device.

Before you begin the sign-in process, confirm the following prerequisites:

• Your organization has a GCC-High tenant with Exchange Online and Azure AD.
• Your user account is licensed for Exchange Online in GCC-High.
• Modern Authentication is enabled on the tenant. GCC-High tenants have this enabled by default.
• You have the full email address assigned by your tenant administrator.
• Outlook Mobile version 4.2340.0 or later is installed on iOS or Android.

Steps to Sign In to a GCC-High Tenant on Outlook Mobile

Follow these steps exactly. If you skip the manual configuration, Outlook Mobile will attempt to connect to the commercial cloud and fail.

1. Open Outlook Mobile and start the Add Account process
   On the welcome screen or after tapping your profile icon, tap Add Account. If you already have an account, tap Settings (gear icon) then Add Account.
2. Enter your full email address
   Type your GCC-High email address. Do not tap the autodiscover suggestion. Tap Continue.
3. Tap Configure Settings Manually
   After Outlook Mobile fails to autodiscover the commercial endpoint, it will show a screen with a link to configure settings manually. Tap that link. If Outlook Mobile does not show this link, close the app, reopen it, and repeat steps 1 and 2. Some versions require you to tap Add Account again and select Exchange directly.
4. Set the server field to outlook.office365.us
   In the manual configuration screen, locate the Server field. Delete any pre-filled value. Type outlook.office365.us exactly. Do not include https:// or a trailing slash.
5. Leave the Domain field blank
   The Domain field is optional for GCC-High. Leave it empty. If your administrator requires a domain, they will provide it separately.
6. Enter your password and tap Sign In
   Type the password for your GCC-High account. Tap Sign In. Outlook Mobile will redirect you to the GCC-High Azure AD login page. You may see a page with login.microsoftonline.us in the address bar. This is correct.
7. Complete Multi-Factor Authentication if prompted
   If your tenant requires MFA, approve the prompt on your registered device or enter the verification code. This step uses the GCC-High Azure AD instance.
8. Grant permissions for Outlook Mobile
   On the consent screen, review the permissions and tap Accept. Outlook Mobile needs access to your mailbox, calendar, and contacts.
9. Wait for synchronization to finish
   Outlook Mobile will sync your mailbox. This may take a few minutes for the first sync. You will see your inbox, calendar, and contacts appear.

If Outlook Mobile Still Cannot Connect to GCC-High

Outlook Mobile says Account Not Found or Wrong Password

This usually means the server field was not set to outlook.office365.us. Remove the account and re-add it using the manual configuration steps above. Double-check that no extra spaces or characters exist in the server field. Also confirm your password has not expired. GCC-High tenants enforce password expiration policies.

Outlook Mobile keeps redirecting to the commercial login page

If you see login.microsoftonline.com instead of login.microsoftonline.us, the account was not configured manually. Remove the account and start again. Tap Configure Settings Manually immediately after entering your email address. Do not let Outlook Mobile attempt autodiscover.

Outlook Mobile shows a sync error after sign-in

This can happen if Modern Authentication is not enabled on the tenant. Check with your administrator that the tenant has Modern Authentication enabled for Exchange Online. Also verify that Outlook Mobile is updated to the latest version from the App Store or Google Play Store. Older versions may not support GCC-High endpoints.

Outlook Mobile cannot find GCC-High calendar or contacts

After successful sign-in, calendar and contacts sync automatically. If they do not appear, force a sync by swiping down on the inbox. If the issue persists, remove the account and re-add it. Make sure your GCC-High mailbox is not a shared mailbox. Shared mailboxes require additional setup in Outlook Mobile.

Item	Commercial Microsoft 365	GCC-High
Exchange ActiveSync endpoint	outlook.office365.com	outlook.office365.us
Azure AD login page	login.microsoftonline.com	login.microsoftonline.us
Autodiscover support in Outlook Mobile	Yes, automatic	No, manual configuration required
Modern Authentication requirement	Optional	Required
Multi-Factor Authentication	Optional	Commonly enforced

Now you can sign in to your GCC-High tenant on Outlook Mobile using the manual server configuration. After the account is set up, test sending and receiving a message to confirm full functionality. For advanced management, consider enabling the Outlook Mobile Security Center to enforce conditional access policies on the device.