How to Resolve “Create Shared Mailbox with Same Alias” Error in Microsoft 365

Creating a shared mailbox in Microsoft 365 is typically straightforward, but you might encounter an error stating that the email address (alias) is unavailable because it’s already in use. This article explains why this issue arises and provides a step-by-step guide to resolve it effectively.

Why Does This Error Occur?

Microsoft 365 requires unique email addresses (aliases) across all mail-enabled objects in a tenant. If the alias you are trying to assign to a new shared mailbox is already being used by another mailbox, group, contact, or resource, the system will block its creation to prevent conflicts.

Steps to Resolve the Issue

To resolve the error, you need to identify the object currently using the alias and decide whether to free up the alias or choose a different one for the new shared mailbox.

Step 1: Identify the Object Using the Alias

Using the Microsoft 365 Admin Center

1. Log in to the Microsoft 365 Admin Center with admin credentials.
2. Search for the Alias:
   • Use the global search bar to look for the alias in Users, Groups, Contacts, and Shared Mailboxes.
3. If the alias is found, note its current usage (e.g., user mailbox, distribution group, or contact).

Using PowerShell for Advanced Search

1. Connect to Exchange Online PowerShell:

• Open PowerShell and connect using:

Connect-ExchangeOnline -UserPrincipalName admin@example.com

2. Run a Search for the Alias:

• Use the following command to find the object:

Get-Recipient -Filter "EmailAddresses -like '*alias@example.com*'"

• Replace alias@example.com with the email address in question.

3. Review Results:

• Identify the type of object (e.g., mailbox, group, or contact) and its current usage.

Step 2: Resolve the Conflict

Option 1: Remove the Alias from the Existing Object

If the alias is no longer needed on the existing object:

1. Modify the Object Using PowerShell:

• Use this command to remove the alias:

Set-Mailbox -Identity "existing-object" -EmailAddresses @{Remove="alias@example.com"}

• Replace existing-object with the name of the object.

2. Verify the Change:

• Confirm the alias has been removed by re-running the Get-Recipient command.

3. Create the Shared Mailbox:

• Use the alias for the new shared mailbox in the Admin Center or via PowerShell.

Option 2: Use a Different Alias for the Shared Mailbox

If the alias is actively in use and cannot be removed:

1. Choose a Unique Alias:

• Select a new, unused email address for the shared mailbox.

2. Create the Shared Mailbox:

• Proceed with the creation using the updated alias.

Additional Tips for Managing Aliases in Microsoft 365

• Use Naming Conventions:
  • Establish a standard for alias creation to avoid duplicates (e.g., departmentname_shared@example.com).
• Regular Audits:
  • Periodically review email aliases to ensure efficient usage and avoid conflicts.
• Document Changes:
  • Maintain records of alias assignments to simplify future troubleshooting.

Frequently Asked Questions

1. Can I reuse an alias immediately after removing it?

Yes, once an alias is removed from an object, it becomes available for use. However, allow a few minutes for the change to propagate across Microsoft 365.

2. What happens if I assign the same alias to multiple objects?

Microsoft 365 will block the assignment and display an error. Unique aliases are required to avoid email delivery issues.

3. Can I assign multiple aliases to a single shared mailbox?

Yes, shared mailboxes can have multiple aliases. You can add them via the Admin Center or PowerShell.

Conclusion

Resolving alias conflicts in Microsoft 365 is straightforward with the right tools and approach. By identifying the object using the alias and taking appropriate action, you can successfully create shared mailboxes without errors. Regular maintenance and clear naming conventions can further streamline alias management.

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