"Target mailbox doesn't have an SMTP proxy matching" error during a mailbox migration

2025-04-24
Applies to: Exchange Online

Symptoms

When you try to migrate on-premises mailboxes to Microsoft Exchange Online in a hybrid environment, you receive the following error message:

The target mailbox doesn't have an smtp proxy matching '<domain>.mail.onmicrosoft.com'

Cause 1

The on-premises mailbox doesn't have an SMTP address that matches <user>@<domain>.mail.onmicrosoft.com.

To check the SMTP addresses for an on-premises mailbox, run the following cmdlet in Exchange Management Shell (EMS):

Get-Mailbox -Identity <user ID> | FL EmailAddresses

Cause 2

The source mailbox has an SMTP address that matches <user>@<domain>.mail.onmicrosoft.com. However, the SMTP address isn't synced to the corresponding mail-user object in Exchange Online.

To check the SMTP addresses for the mail-user object in Exchange Online, run the following cmdlet in Exchange Online PowerShell:

Get-MailUser -Identity <user ID> | Select -ExpandProperty EmailAddresses

Resolution for Cause 1

Use the following steps to add a secondary SMTP address that matches<user>@<domain>.mail.onmicrosoft.com to the on-premises mailbox:

Run the following PowerShell cmdlet in EMS to check whether the on-premises mailbox has an email address policy:
```
Get-Mailbox <user ID> | FL EmailAddressPolicyEnabled
```
If the on-premises mailbox has an email address policy, the value of the EmailAddressPolicyEnabled parameter is True.

You can also use the Exchange admin center (EAC) to check whether an on-premises mailbox has an email address policy. A policy exists if the option Automatically update email addresses based on the email address policy applied to this recipient is selected for the user.

Note

To check the email address templates for the policy, run the following PowerShell cmdlet in EMS: Get-EmailAddressPolicy | FL Identity, EnabledEmailAddressTemplates
If the on-premises mailbox has an email address policy, follow these steps:
- In the EAC for Exchange Server, select Mail flow, and then select Email address policies.
- Select the email address policy that you want to change, and then click Edit.
- In Email address format, add the <domain>.mail.onmicrosoft.com domain to the policy, select Save, and then select Apply to apply the change to the recipients.
- Run the following PowerShell cmdlet in EMS to verify that the on-premises mailbox now has an SMTP address that matches<user>@<domain>.mail.onmicrosoft.com:
```
Get-Mailbox <user ID> | FL EmailAddresses
```
Note

For more information, see Email address policies in Exchange Server.
If the on-premises mailbox doesn't have an email address policy, or step 2 fails, follow these steps:
- In the EAC for Exchange Server, select Recipients, and then select Mailboxes.
- Select and double-click the on-premises mailbox that you want to change.
- In Email addresses, select the add icon, and then add an SMTP address that matches<user>@<domain>.mail.onmicrosoft.com.
- Select OK, and then select Save.
- Run the following PowerShell cmdlet in EMS to verify that the on-premises mailbox now has an SMTP address that matches<user>@<domain>.mail.onmicrosoft.com:
```
Get-Mailbox <user ID> | FL EmailAddresses, EmailAddressPolicyEnabled
```
Wait for directory sync to run, or force a delta directory sync, to push the change to Microsoft Entra ID.

Resolution for Cause 2

Check for directory sync errors in Microsoft Entra Connect or the Microsoft 365 admin center. For information about how to identify and fix directory sync errors, see Monitor Microsoft Entra Connect Sync with Microsoft Entra Connect Health and View directory synchronization errors in Microsoft 365.

If you don't find directory sync errors, perform the following checks:

Run the following PowerShell cmdlet to check whether the user object in Microsoft Entra ID has a validation error:

Install-Module -Name Microsoft.Entra 
Connect-Entra -Scopes 'User.Read.All'
(Get-EntraUser -Filter "startsWith(DisplayName, '<user display name>')").serviceProvisioningErrors.errorDetail

Identify and resolve any user validation errors.

Run the following PowerShell cmdlet to check whether the user object in Microsoft Entra ID has an SMTP address that matches<user>@<domain>.mail.onmicrosoft.com:
```
(Get-EntraUser -Filter "startsWith(DisplayName, '<user display name>')").ProxyAddresses
```
Run the following PowerShell cmdlet in Exchange Online PowerShell to check whether the user object in Exchange Online has an SMTP address that matches<user>@<domain>.mail.onmicrosoft.com:
```
Get-MailUser -Identity <user ID> | Select -ExpandProperty EmailAddresses
```
If you find that the user object in Exchange Online doesn't have a SMTP address that matches<user>@<domain>.mail.onmicrosoft.com but the user object in Microsoft Entra ID does, there might be a sync issue between Microsoft Entra ID and Exchange Online.
Verify that the <domain>.mail.onmicrosoft.com domain is an accepted domain in Exchange Online. For more information about the coexistence domain that's added by the Hybrid Configuration Wizard, see Hybrid configuration options.

If you're still unable to fix the issue, contact Microsoft Support for assistance.

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