Contact Problems

Fix Microsoft Multitenant Collaboration Mail Attribute Mapping Issues

Steve K Sep 28, 2026 868 views

Question details

Users from one Microsoft tenant appear in Outlook's Global Address List with guest UPNs instead of their actual email addresses during multitenant collaboration.

How to Fix Microsoft Multitenant Collaboration Mail Attribute Mapping Issues

Product: Microsoft 365 / Outlook
Device & OS: not provided
Scenario: Collaborating in a Microsoft multitenant environment and viewing contacts in Outlook.
Observed behavior: Outlook's Global Address List displays guest UPNs rather than correct email addresses due to directory synchronization or attribute-mapping configuration errors.

Before you start

Ensure you have Global Administrator or Exchange Administrator privileges in your Microsoft 365 tenant, as resolving directory synchronization and cross-tenant attribute mapping issues requires backend administrative access.

Solution 1Recommended

Create a Service Request in the Microsoft 365 Admin Center

Since multitenant mail attribute mapping involves backend directory synchronization and cross-tenant permissions, creating a support request is the most direct way to resolve the configuration conflict.

Resolving guest UPN display issues in the Global Address List requires specialized tools that only Microsoft support teams and tenant administrators can access. By opening a service request, the support team can directly investigate your tenant permissions, directory synchronization status, and mail attributes.

Log in to the Admin Center

Navigate to the Microsoft 365 admin center in your web browser and sign in using an account with administrator privileges.

Navigate to Help & Support

On the left-hand navigation menu, click on 'Support' and then select 'Help & support' or 'Service requests'.

Describe the Mapping Issue

In the issue description box, explain that users from a multitenant collaboration environment are appearing in the Outlook Global Address List with guest UPNs instead of email addresses.

Submit the Service Request

Follow the on-screen prompts to submit the ticket. A dedicated support engineer will contact you to investigate the directory synchronization and attribute mapping.

Create a Service Request in the Microsoft 365 Admin Center

Administrator Access Required: Standard users cannot access the Service Requests area. If you do not see the Support option, you must contact your organization's IT department to open the ticket on your behalf.

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Frequently Asked Questions

Why do guest UPNs show up instead of email addresses in Outlook?

This typically happens due to incorrect attribute-mapping configurations or directory synchronization errors between interacting tenants in a Microsoft multitenant environment.

Can a standard user fix the Global Address List mail attribute issue?

No, correcting multitenant synchronization and attribute mapping requires high-level administrative access to the Microsoft 365 admin center. Standard users must report the issue to their IT administrators.

How long does it take for Global Address List changes to sync?

After an administrator or Microsoft support corrects the attribute mapping, it can take anywhere from a few hours up to 24 hours for the Global Address List (GAL) to fully synchronize and update across all Outlook desktop clients.

Outlook & Email Problems