Security Policy Errors

How to Fix Microsoft Loop Using an onmicrosoft.com Address

Steve K Sep 28, 2026 868 views

Question details

Users experience an issue in Microsoft Loop where task assignments default to an onmicrosoft.com address instead of the configured custom domain, triggering IT policy errors.

How to Fix Microsoft Loop Using an onmicrosoft.com Address Error

Product: Microsoft Loop
Device & OS: not provided
Scenario: Assigning a task within Microsoft Loop using a custom domain configuration.
Observed behavior: Microsoft Loop defaults to the onmicrosoft.com address rather than the custom domain, resulting in an IT policy error.

Before you start

Verify that your custom domain is properly configured and set as the default domain in the Microsoft 365 admin center before escalating the issue.

Solution 1Recommended

Open a Support Request via Microsoft 365 Admin Center

Since standard troubleshooting does not resolve this routing issue, a Microsoft 365 administrator must contact Microsoft Support to investigate the backend account configuration.

This error typically points to a backend synchronization failure where Microsoft Loop does not recognize the custom domain policy. Microsoft Support has the necessary access to inspect service logs and correct the tenant configuration.

Identify your Administrator

Locate your organization's Microsoft 365 administrator, which is typically your IT department or the person who manages your company's email services.

Log into the Admin Center

Ask the administrator to sign in to the Microsoft 365 admin center using their admin credentials.

Navigate to Support

Click on the 'Show all' menu on the left navigation pane, then select 'Support' followed by 'Help & support'.

Submit a Request

Describe the issue regarding Microsoft Loop defaulting to the onmicrosoft.com address during task assignment and submit the ticket so Microsoft Support can review the backend service logs.

Open a Support Request via Microsoft 365 Admin Center

Administrator Access Required: End-users cannot open these specific backend support requests. You must have admin privileges to access the Microsoft 365 admin center.

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Frequently Asked Questions

Why does Microsoft Loop use the onmicrosoft.com address instead of my custom domain?

This happens when the Microsoft 365 backend fails to properly sync your custom domain to specific applications like Loop, causing it to fall back to the default tenant routing address.

Can an end-user fix this domain assignment issue directly?

No. Because this issue involves tenant-level domain routing and backend synchronization logs, only a designated Microsoft 365 administrator can escalate and resolve it via Microsoft Support.

How do I find out who my Microsoft 365 administrator is?

Your administrator is typically the person or IT department that provided your work email account. You can also log into your Microsoft account profile settings to view your organization's IT contact information.

Microsoft Office Security Issues