Outlook Error Codes

How to Fix Exchange Online Error 550 5.0.350 Fake Sender

Maira Mehtab Sep 22, 2026 868 views

Question details

The user is trying to resolve an email delivery failure where messages are rejected by a remote server with a fake sender notification.

Product: Exchange Online
Device & OS: not provided
Scenario: Sending emails to specific recipients or domains where the message fails to deliver and bounces back.
Observed behavior: The remote server rejects the email, returning a Non-Delivery Report (NDR) containing the message: 550 5.0.350 Requested mail action not taken: Fake sender.

Before you start

Before troubleshooting, ensure you have administrative access to the Microsoft Exchange Admin Center and have the complete Non-Delivery Report (NDR) saved for reference.

Solution 1Recommended

Analyze the Non-Delivery Report and Run a Message Trace

Use the Exchange Admin Center to trace the failed message and review the full NDR to identify if the issue is isolated to a specific domain or affecting multiple users.

Running a message trace helps determine the exact path of the email and where it was rejected. Reviewing the NDR provides specific diagnostic codes needed for resolution.

Review the NDR

Open the complete Non-Delivery Report (NDR) to identify the exact sender, recipient, and affected domain without sharing sensitive information publicly.

Access Exchange Admin Center

Navigate to Message Trace

Go to the Mail flow section in the left-hand menu and select Message trace.

Run the Trace

Enter the sender and recipient details to trace the delivery path of the rejected email and execute the search.

Analyze the Results

Check the trace results to see whether the 550 5.0.350 error affects all recipients, a specific email address, or an entire remote domain.

Solution 2

Consult Microsoft Guidance and Contact Support

If analyzing the trace does not resolve the root cause, you will need to review official Microsoft documentation or escalate the issue to Microsoft Support.

Free Microsoft Office alternative

Looking for a Hassle-Free Office Suite? Try WPS Office

While Exchange Online email delivery errors require server-side troubleshooting, managing your documents shouldn't be complicated. WPS Office is a lightweight, free alternative to Microsoft Office, offering an intuitive experience for Word, Excel, and PowerPoint files.

1. Visit the Website: Go to the official WPS Office website.
2. Download the Installer: Click the Free Download button to get the setup file.
3. Install and Launch: Run the downloaded installer and follow the on-screen instructions to set up WPS Office on your computer.

Fully compatible with Microsoft Office formats like DOCX, XLSX, and PPTX.Lightweight application that doesn't consume excessive system resources.Familiar user interface for a seamless transition with zero learning curve.Completely free to use with built-in PDF editing tools and templates.

Frequently Asked Questions

What does Error 550 5.0.350 mean in Exchange Online?

This error indicates that your email was rejected by the recipient's remote mail server because it classified the sender as a fake sender. This often happens due to strict anti-spam filters or misconfigured email authentication records.

Can I fix the 550 5.0.350 error without administrator rights?

Generally, no. Fixing this error usually requires accessing the Exchange Admin Center to run a message trace and reviewing domain configurations, which requires administrative privileges. Regular users should forward the Non-Delivery Report (NDR) to their IT support team.

How do I prevent my emails from being marked as a fake sender?

Ensure your domain's SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC records are correctly configured and up-to-date in your DNS settings. This verifies your domain's identity to remote servers and greatly improves email deliverability.

Microsoft Office Error Codes