How to Troubleshoot SAP Mail Relay Failing for One Exchange Online User
Question details
SAP mail relay configured through an on-premises Exchange server fails to deliver emails to a single Exchange Online user, with no tracking results available.
- Product
- Microsoft Exchange Server
- Device & OS
- not provided
- Scenario
- Relaying automated emails from an SAP environment through an on-premises Exchange server to an Exchange Online mailbox in a hybrid setup.
- Observed behavior
- The mail relay successfully processes messages for most users but consistently fails for one specific Exchange Online user. Both message tracking and message trace tools yield zero results for the failed deliveries.
Verify that the affected Exchange Online user's mailbox is active, properly licensed, and can successfully receive standard emails directly from other internal and external senders before modifying your SAP relay configurations.
Review Exchange Connectors and Consult Microsoft Q&A Support
Because the email drops before a trace ID is generated, the issue lies within the on-premises routing, connector permissions, or recipient configurations.
When an email fails to appear in an Exchange Online message trace, it usually indicates that the on-premises Exchange server rejected the message or failed to route it properly to the cloud.
Resolving this requires deep inspection of hybrid transport rules, target addresses, and raw SMTP logs.
Open the Exchange Management Shell on your on-premises server and run 'Get-RemoteMailbox -Identity <User> | fl TargetAddress'. Ensure the routing address correctly points to your tenant's routing domain (e.g., user@tenant.mail.onmicrosoft.com).
In the Exchange Admin Center, navigate to 'mail flow' > 'receive connectors'. Confirm that the connector handling SAP traffic has the correct IP scopes and permissions to relay messages to the external/cloud environment.
Turn on protocol logging for your SAP-facing Receive Connector and your Office 365 Send Connector. Reproduce the SAP email failure and review the generated logs in the Exchange transport logging directory to identify exact SMTP error codes.
Navigate to the official Microsoft Q&A forum and post your issue under the 'Exchange Server' tag. Include your sanitized protocol logs, connector configurations, and the exact SMTP error code for specialized assistance from Exchange experts.
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Frequently Asked Questions
Why does message trace show no results for this specific Exchange Online user?
If message tracking and message trace show no results, the email is likely failing at the point of origin (SAP) or being immediately rejected by the on-premises Exchange Receive Connector before an Exchange message ID can be generated.
How can I verify if the affected user's hybrid routing is misconfigured?
Use the Exchange Management Shell on your on-premises server to check the user's TargetAddress property. If it does not point to your organization's verified '.mail.onmicrosoft.com' routing domain, the on-premises server will not know how to forward the message to Exchange Online.
Can a corrupted Active Directory contact cause isolated mail relay failures?
Yes. If the specific user's remote mailbox object in the on-premises Active Directory is misconfigured, unlinked, or corrupted, the on-premises Exchange server will treat the destination as unreachable and drop the incoming SAP emails for that user.
