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Fix Microsoft 365 Email Error 550 5.7.708 Sent Through Gmail
Question details
The user needs to resolve an email rejection issue where Microsoft 365 blocks messages sent through Gmail with Exchange Online Error 550 5.7.708.
- Product
- Microsoft 365 / Exchange Online
- Device & OS
- not provided
- Scenario
- Sending emails via Gmail's 'Send mail as' feature using a Microsoft 365 account.
- Observed behavior
- Messages are rejected with the Error 550 5.7.708 because Microsoft is blocking traffic from the originating Gmail or relay IP address.
Ensure you have your Microsoft 365 account credentials ready and can access Outlook on the web for diagnostic testing.
Test Direct Sending via Outlook on the Web
Determine if the block is specific to Gmail's SMTP path or affects your entire Microsoft 365 tenant.
Before proceeding with IP delisting, it is critical to verify where the block is occurring. Testing directly through Microsoft's webmail bypasses the Gmail relay servers.
Navigate to outlook.office.com in your web browser and sign in using your Microsoft 365 credentials.
Click 'New message' and send a test email to another address you own to see if it delivers successfully.
If the message sends successfully, the issue is related to Gmail's sending IP. If it fails with the same error, your Microsoft 365 tenant IP is blocked.
Request IP Delisting or Contact Microsoft Support
Use Microsoft's delisting portal or open a support request to unblock the sending IP address.
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Frequently Asked Questions
What does Exchange Online Error 550 5.7.708 mean?
This error indicates that Microsoft Exchange Online is rejecting outgoing emails because the traffic is originating from a blocked or suspicious IP address, often associated with a trial tenant or flagged relay server.
Why does this error happen specifically when using Gmail's 'Send mail as' feature?
Microsoft 365 may detect the shared Google SMTP relay servers as a source of spam if other users have abused them. This triggers automated security filters that temporarily block the Gmail IP address from sending mail through your Microsoft tenant.
How long does the Microsoft IP delisting process take?
Once you submit a delisting request through the Microsoft Anti-Spam IP Delist Portal or via a support ticket, it typically takes between 1 to 24 hours for the IP address to be cleared and email flow to restore.
