Fix email delivery issues for error code 5.4.6 through 5.4.20 in Office 365

Here's what to do if you get delivery status notification (DSN) error code 5.4.6 or Exchange NDR 5.4.6 through 5.4.20 in a non-delivery report (NDR). There can be several causes for dsn error code 5.4.6, but this might happen if the message hop count is exceeded or the route through which the message gets delivered is broken. Some causes and solutions for hop count being exceeded are provided later in this topic. The information here applies to a range of error codes 5.4.6 through 5.4.20.

Finding information about Exchange NDR 5.4.x that will help you solve the problem

Use the information in the Exchange NDR to decide how to fix the problem.

Tips for fixing the problem that is causing Exchange NDR 5.4.6

Here are some procedures that you can try that may 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.

Accepted domain issues

Verify that the recipient's domain is configured as an authoritative accepted domain in Exchange Online. For more information, see Manage Accepted Domains in Exchange Online.

Hybrid configuration issues

If your domain is part of a hybrid deployment between Exchange and Exchange Online, check the following items based on your configuration:

You route all incoming mail for your hybrid domain through Exchange Online.

This error can happen when the MX record for your hybrid domain points to Exchange Online, and the Outbound connector that's used to route mail to your on-premises Exchange organization is configured to use DNS routing.

To fix the problem, configure a dedicated Outbound connector that uses smart host routing and that has your on-premises hybrid server configured as a smart host. The easiest way to fix the problem is to re-run the Hybrid Configuration Wizard in the on-premises Exchange organization. Or, you can verify the configuration of the Outbound connector that's used for hybrid by following these steps:
1. Open the Office 365 portal at https://portal.office.com, and then click Admin > Exchange.
2. In the Exchange admin center, click Mail Flow > Connectors. In the Outbound connectors section, select the connector that's used for hybrid, and then click Edit.
3. On the Delivery tab, verify that Route mail through smart hosts is selected and that the correct IP address or fully qualified domain name (FQDN) is specified for the smart host.
You route all outgoing mail from Exchange Online through your on-premises hybrid server.

This configuration is controlled by the value of the RouteAllMessagesViaOnPremises parameter on the Outbound connector that's used for hybrid. When the value of this parameter is $true for that connector, you're routing all outgoing mail from Exchange Online through your on-premises hybrid server. You can verify this value by running the following command.
Get-OutboundConnector <ConnectorIdentity> | Format-List Name,RouteAllMessagesViaOnPremises
In this configuration, the error is caused by either of the following items:
- You don't have an Inbound connector that has a Connector Type value of On-premises.
- The Inbound connector that's used for hybrid is scoped to one or more accepted domains.
To fix the problem, configure a dedicated Inbound connector that has a Connector Type value of On-premises and that's not scoped to any accepted domains. The easiest way to fix the problem is to re-run the Hybrid Configuration Wizard in the on-premises Exchange organization. Or, you can verify the configuration of the Inbound connector that's used for hybrid by following these steps:
1. Open the Office 365 portal at https://portal.office.com, and then click Admin > Exchange.
2. In the Exchange admin center, click Mail Flow > Connectors. In the Inbound connectors section, select the connector that's used for hybrid, and then click Edit . Verify the following information:
  - General Verify that On-premises is selected.
  - Scope Verify that Accepted domains is empty.

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

Causes for NDR 5.4.6 and what does this error mean? Could be related to hop count exceeded

There are two likely possibilities:

Based on the domain in the recipient's email address, your Exchange Online organization accepted the message, but then couldn't correctly route the message to the recipient. This is likely caused by accepted domain setup issues.
In hybrid environments, there are misconfigured connectors in your Exchange Online organization.

Details about this Exchange NDR, related to hop count exceeded

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

User information section
- Delivery has failed to these recipients or groups:
  
  <email addresses>
  
  A problem occurred while delivering this message to this email address. Try sending this message again.
- The outbound connection attempt was not answered because either the remote system was busy or it was unable to take delivery of the message.
Diagnostic information for administrators section
- #5.4.6 smtp;554 5.4.6 Hop count exceeded - possible mail loop> #SMTP#