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Fix Gmail to Microsoft 365 Migration Routing Error 450 4.7.26
Question details
The user needs to resolve an SMTP routing failure occurring during a staged email migration from Google Workspace to Exchange Online.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Performing a staged email migration from Gmail to Microsoft 365 where Exchange Online Protection blocks incoming mail.
- Observed behavior
- Microsoft 365 rejects incoming IPv6 mail from Gmail with SMTP error 450 4.7.26, indicating a DKIM body-hash failure or failed SPF authorization.
Ensure you have administrative access to both your Google Workspace admin console and the Microsoft 365 Exchange admin center, as well as access to modify your domain's DNS records.
Validate and Update SPF and DKIM DNS Records
Ensure that your domain's DNS records correctly authorize both Gmail and Microsoft 365 senders to prevent Exchange Online Protection from rejecting the emails.
Error 450 4.7.26 indicates that the message sent over IPv6 is failing Sender Policy Framework (SPF) or DomainKeys Identified Mail (DKIM) validation. Configuring both correctly ensures the destination server trusts the email source.
Log in to your domain registrar's DNS management portal and ensure your SPF TXT record includes both Google Workspace and Microsoft 365 IP addresses (e.g., v=spf1 include:_spf.google.com include:spf.protection.outlook.com ~all).
Log in to the Google Workspace Admin console, navigate to Apps > Google Workspace > Gmail > Authenticate email, and ensure DKIM is enabled with the correct selector.
Check that the DKIM TXT record in your DNS portal exactly matches the value generated by the Google Workspace Admin console.
Review Email Routing Rules and Microsoft 365 Connectors
Prevent DKIM body-hash failures by ensuring no intermediate routing rules modify the email body or headers after it is signed.
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Frequently Asked Questions
What does SMTP error 450 4.7.26 mean in Microsoft 365?
This error indicates that Microsoft Exchange Online Protection is temporarily rejecting incoming mail, typically over IPv6, because the message failed SPF (Sender Policy Framework) or DKIM (DomainKeys Identified Mail) authentication checks.
Why does a DKIM body-hash failure occur during a staged migration?
A DKIM body-hash failure happens when the email's content or headers are modified after the DKIM signature is applied by the sender. During migration, this is often caused by intermediate routing rules, anti-spam filters, or automatic disclaimers adding text to the message before it reaches Microsoft 365.
How can I fix the IPv6 inbound mail flow rejection in Exchange Online?
Ensure that your SPF record explicitly includes both the Google Workspace and Microsoft 365 IP addresses. Additionally, verify that your inbound connectors in the Exchange admin center are correctly configured to trust the migration path and that DKIM is strictly aligned.
