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Fix Outlook Global Address List Showing UPN Instead of Email
Question details
External users are appearing with a guest UPN format instead of their actual email address in the Outlook Global Address List.
- Product
- Microsoft Outlook / Microsoft 365
- Device & OS
- not provided
- Scenario
- Collaborating in a multitenant Microsoft 365 environment where cross-tenant synchronization shares address lists.
- Observed behavior
- The Global Address List (GAL) correctly displays some external users but lists others with a guest UPN (e.g., user#Ext#@domain.onmicrosoft.com) instead of their standard email address.
Ensure you have global administrator or Exchange administrator credentials for your Microsoft 365 tenant, as resolving directory synchronization issues requires admin access.
Open a Service Request in the Microsoft 365 Admin Center
Because this issue involves cross-tenant synchronization, directory permissions, and Global Address List attribute mapping, it requires Microsoft Support to inspect and correct the tenant configuration.
In a multi-tenant environment, Azure Active Directory creates guest user accounts with a '#Ext#' UPN. If the address-list attribute mapping or tenant permissions are misconfigured, Outlook may display this raw UPN instead of mapping it to the primary SMTP address. Modifying these backend cross-tenant sync parameters often requires specialized diagnostic tools available only to Microsoft Support.
Log into the Microsoft 365 admin center using an account with administrator privileges.
On the left-hand navigation menu, click on the 'Support' dropdown and select 'Help & support'.
In the search bar, type a brief description such as 'Global Address List shows UPN for external users' and press Enter to view automated diagnostic checks.
If the automated solutions do not resolve the issue, click the headset icon or the 'Contact Support' button at the bottom of the pane to open a new service request.
Fill out the support form detailing your multitenant setup and provide specific examples of the affected guest UPNs (e.g., user#Ext#@domain.onmicrosoft.com) so the support engineer can investigate the directory permissions and GAL mapping.
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Frequently Asked Questions
Why does Outlook show a UPN with '#Ext#' instead of a standard email address?
When a guest user is added to a Microsoft 365 tenant, Azure Active Directory generates a unique guest User Principal Name (UPN) containing '#Ext#'. If attribute mapping fails or synchronization delays occur, the Global Address List will default to displaying this backend UPN instead of resolving their actual SMTP email address.
Can an end-user fix the Global Address List displaying UPNs?
No, this is a server-side synchronization and tenant configuration issue. End-users cannot modify Global Address List mappings or cross-tenant synchronization policies; an IT administrator must resolve this via the Microsoft 365 admin center.
How long does it take for Global Address List changes to sync to my Outlook desktop app?
Once Microsoft Support or your IT administrator corrects the attribute mapping, it typically takes 24 to 48 hours for the changes to fully propagate across the Microsoft 365 environment and update the Offline Address Book (OAB) downloaded by your local Outlook client.
