Fix External SMTP Email Delivery Failure After Changing User Address
Question details
External devices and applications fail to send emails to users who recently had their email addresses changed.
- Product
- Microsoft Exchange and Azure Active Directory
- Device & OS
- not provided
- Scenario
- Attempting to use scan-to-email devices, printer cloud services, or other external applications to deliver messages via SMTP to a recently updated user email address.
- Observed behavior
- Emails sent internally from Outlook deliver successfully, but external SMTP applications fail to deliver messages to the updated address due to Azure Active Directory synchronization errors with the SMTP proxy addresses.
Ensure you have administrative privileges to access your local Active Directory Users and Computers (ADUC) and the Microsoft 365 Admin Center.
Verify and Synchronize Azure AD SMTP Attributes
Use the Microsoft IdFix tool to identify directory synchronization errors and force an update to Azure Active Directory.
When an email address is changed, the local Active Directory attributes must correctly sync with Azure Active Directory. If the SMTP proxyAddresses attribute is malformed or fails to sync, external applications relying on Azure AD routing will bounce the emails.
Open Active Directory Users and Computers (ADUC) on your domain controller. Navigate to the affected user's properties, open the Attribute Editor tab, and ensure the 'proxyAddresses' value contains the correct primary SMTP address formatted as 'SMTP:newaddress@domain.com'.
Download and launch the Microsoft IdFix DirSync Tool. Click 'Query' to scan your local directory for synchronization errors, particularly focusing on duplicate or invalid proxy addresses for the affected users.
Select the appropriate 'Action' (such as Edit or Remove) for any identified errors in the IdFix tool and click 'Apply'. Once resolved, open PowerShell and run 'Start-ADSyncSyncCycle -PolicyType Delta' to force a synchronization with Azure AD.
Wait a few minutes for the synchronization to complete. Go to your scan-to-email device or external application and send a test message by manually typing out the user's complete, newly updated email address.
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Frequently Asked Questions
Why does Outlook send emails properly while external SMTP devices fail?
Outlook utilizes internal Exchange routing, which immediately recognizes account changes in the local or cached directory. External devices rely on SMTP routing through Azure Active Directory, which fails if the new SMTP proxy addresses haven't successfully synchronized to the cloud.
What is the Microsoft IdFix tool used for?
The Microsoft IdFix DirSync tool is designed to help Active Directory administrators identify and remediate identity object errors (like invalid characters or duplicate proxyAddresses) in an on-premises Active Directory before syncing them to Azure AD.
How long does it take for proxy address changes to reflect in Microsoft 365?
By default, Azure AD Connect runs a synchronization cycle every 30 minutes. Once synced, it may take an additional 5 to 15 minutes for Exchange Online routing to fully recognize the updated SMTP proxy addresses.
