Fix email delivery issues for error code 550 4.4.7 in Office 365

This topic can help you fix email problems that are associated with error code 550 4.4.7 if you see this in a non-delivery report (NDR). Mail flow problems can be frustrating, but we have solutions you can try in order to get your message sent.

There can be several causes for dsn error code 4.4.7, so use the information in the NDR to decide how to fix the problem. For more details about the causes, see Causes for 4.4.7, later in this topic.

email user symbol

I sent a message, what can I do to fix this?

Administrator symbol

I'm the Admin, what can I do to fix this?

Help symbol

Why did I get a non-delivery report?

email user symbol

I sent a message and got error code 4.4.7 in an NDR. What can I do to fix this?   

Here are some procedures that you can try that might allow you to resend the message successfully. Message delivery from server-to-server can be complicated or require special access to settings, so most of these steps are designed for an Office 365 email administrator and not the average email sender. If the steps here don’t help, contact your email administrator and refer them to this information so they can try to resolve the issue for you.

Problems in the destination domain

If you get DSN error code 4.4.7 and have problems sending email to recipients in one domain only, the problem is likely with that destination domain. A domain is similar to an organization name or the name of an email provider and in an email address it shows up on the right-hand side of the at symbol (@). For example, in is the domain name. Learn more about domains at What are domain names? Possible causes for domain issues include:

  • Temporary network or Internet connection issues in the destination domain.

  • Aggressive anti-spam settings in the destination domain that block legitimate senders, for example, all senders from any domain in Exchange Online.

If you suspect the problem is with the destination domain, let the administrators of that domain know. You need to provide the following information, which is all contained in the NDR:

  • The name of the mail server in the destination domain, and the error message returned by the mail server.

  • The number of delivery attempts made by your email server, an Exchange Online source server, and how long it tried to reach the remote server.

The administrators in the destination domain will need to investigate what's happening. Possible solutions may include:

  • Stop blocking messages from Exchange Online, or specifically allow messages from senders in your domain.

  • Contact the support channels for their mail server software or their hosted email service. Office 365 support may also be able to help.

Administrator symbol

I'm the email admin. What can I do to fix NDR 4.4.7 issues?   

If the steps in the email user help section don't solve the issue for the sender, the solution might be related to the way the user's Office 365 domain is set up. If you have a hybrid topology, the solution might also be related to the on-premises configuration. Here are 5 solutions you can try. You might not need to try all of them to get the message sent successfully.

  • Solution 1: The mail exchange (MX) record for your domain may be missing or incorrect.    Get more information about how MX records work within the domain name system (DNS) at DNS basics.

    Solution 2: You can test your MX record and your ability to send mail    from your organization by using the Verify MX Record and Outbound Connector Test at Office 365 > Mail Flow Configuration in the Microsoft Remote Connectivity Analyzer.

  • Solution 3: The Sender Policy Framework (SPF) record for your domain may be incomplete   , and may not include all sources of mail for your domain. For more information about verifying your SPF record, see Customize an SPF Record to Validate Outbound Email Sent from Your Domain.

  • Soluion 4: Your domain may have expired    due to non-payment. Verify with your domain registrar that your domain is active and not expired.

Solution 5: Hybrid deployment configuration issues.    If your domain is part of a hybrid deployment between Exchange and Exchange Online, and the recipient is in the on-premises organization, there may be a problem with the hybrid configuration. Give the information in the NDR to your on-premises Exchange administrators. They may need to run the Hybrid Configuration Wizard again due to changes in the on-premises IP addresses or firewall rules.

For more information about transport routing in hybrid deployments, see Transport Routing in Exchange 2013 Hybrid Deployments.

Help symbol

Why you got a non-delivery report with error code 4.4.7   

When Exchange Online attempts to deliver a message, the mail server that generated the error might be unable or unwilling to accept the message. This can result in a 4.x.x code being sent back. A 4.x.x code indicates a temporary error. The server doesn't reject the message with a 5. x.x permanent error code, so the recipient doesn't immediately receive an NDR. Instead, Exchange Online repeatedly tries to deliver the message over two days. Only after two days of unsuccessful delivery attempts does the recipient receive this NDR.

The possible causes of this error are:

  • The server is offline or unreachable.

  • The server won't accept delivery of the message.

  • A network problem is causing delivery of the message to time-out.

The Exchange Online non-delivery report (NDR) notification for this specific error may contain some or all of the following information:

  • User information section   

    • The server has tried to deliver this message, without success, and has stopped trying. Please try sending this message again. If the problem continues, contact your helpdesk.

  • Diagnostic information for administrators section   

    • #550 4.4.7 QUEUE.Expired; message expired ##

    • The message was considered too old by the rejecting system, either because it remained on that host too long or because the time-to-live value specified by the sender of the message was exceeded.

    • 450 4.7.0 Proxy session setup failed on Frontend with '451 4.4.0 Primary target IP address responded with ...   Be sure to record the error that follows this string and the last end point attempted.

Still need help with error code 4.4.7?

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See Also

What are Exchange NDRs in Exchange Online and Office 365

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