This table lists the SMTP Error codes that are generated along with bounced mail or other common email failures. These messages might also be seen on the Message Audit report generated in the McAfee Console. 

Error message

Meaning/Guidance to resolve

451 All MX Servers are Unavailable

This error indicates that all MX servers were unreachable for the destination. If you are receiving this error sending mail to a domain, verify that DNS servers are reliably responding.

NOTE: If DNS servers are intermittently failing, the verification you perform at that moment may not be indicative of the performance at the time the message was sent. If this error has happened when mail was being sent to your domain filtered by the McAfee service, this indicates that we are not able to reach your Inbound Server. In this scenario, confirm that the destination server is reachable or engaged your Disaster Recovery service.

550 5.1.1 User Unknown

This error is generated by the destination server that is receiving the mail. This indicates that a mailbox on that server is currently unavailable. This error can be generated both on the receiving and sending of email through the SaaS Email Protection service.

451 Connection Error

This error occurs when there is a problem in delivery of the email message. It indicates that the mail server was reachable and started reception of the message but terminated the delivery before the message transaction could be completed. In this case, the destination server logs should be reviewed to look for any issues causing the abnormal termination of the message transmission.

451 Unknown Error Sending Data

This error occurs when there is a problem in delivery of the email message. It indicates that the mail server was reachable and started reception of the message but terminated the delivery before the message transaction could be completed. In this case, the destination server logs should be reviewed to look for any issues causing the abnormal termination of the message transmission.

451 Validating Sender

This can often occur if the receiving server is utilizing SPF checking. If the destination server has mail filtered by McAfee inbound, disable SPF checking. If this is an issue sending mail to a domain outbound through the McAfee service, review and add McAfee to your SPF record. 

451 Connection Refused

This error indicates that the receiving server is blocking or dropping the connection to McAfee without any response being provided. Unlike unable to locate MX server errors, this indicates that DNS has provided a valid MX record for the domain but the server listed in the MX record is not responding. The receiving server should validate at the firewall and server level that there is not any blocking of McAfee's IP ranges in place.

451 Exceeding connection limit: RBLDNSD

This error is caused by a filter which detects Snowshoe/Hailstorm types of spam attacks, where many hundreds of thousands of messages are delivered in a short period of time from a relatively unknown IP address. The Email Protection Inbound Spam Classification window includes an option labeled "Enable spam flood prevention". Enabling this option helps reduce the chance of receiving spam email messages from short lived spam campaigns known as Hailstorm or Snowshoe attacks. The feature can be disabled by unchecking the Inbound Policy > Spam tab > Enable spam flood prevention box.

452 Validating Sender

Often this error also returns 4.3.1 Insufficient System Resources. This is generated by the receiving server and is often an issue with Exchange 2007's Back Pressure feature.

5.1.0 Address Rejected

This error is not generated by McAfee's Email Protection system. It is generated on the recipient server. This can be due to the email mailbox not existing on the receiving server, filtering policies on the receiving server or the mailbox being unavailable at the time of transmission. If this is received the sender will need to contact the recipient directly to resolve this issue. Adding the sender/recipient to your Allow List will not resolve this issue as it was not generated by McAfee.

5.3.4 Message Size Exceeds Fixed Maximum

This is not an error generated by the McAfee Email Protection service. This is an error generated by the receiving server that indicates that the message has violated some level of attachment size filtering present on that server. McAfee errors related to attachment size will state Attachment Policy in the rejection notification. To resolve this error, the system administrator for the receiving server will need to investigate filtering policies present on that server.

554 Denied

This error indicates that the message was rejected due to policy on the McAfee Email Protection service. Most commonly, this is for a high (more than 99%) spam score of the message being sent. Adding this sender to your McAfee Email Protection user-level Allow List will allow these messages to be delivered.

554 Denied [CS]

This error indicates that the message was rejected as critical spam (Spam Score >=0.99999999). There are no customer options - the messages will be denied regardless of the default policy actions. Adding this sender to your McAfee Email Protection Allow List (account wide or user-level) will allow these messages to be delivered.

554 Message Denied: RBLDNSD

The error is generated based on the sender IP address reputation and mail volume coming from this IP address. Mail flow volume thresholds are determined by using reputation data and adjusted real-time to prevent false positives. The reputation source and volume information is proprietary. The feature can be disabled by unchecking the Inbound Policy > Spam tab > Enable real-time block lists box.

554 Denied [IPR]

The error is generated when sender's IP address is on McAfee's internal IP reputation (IPR) list. This might be caused by high spam traffic from the IP passing through McAfee filters. The IP is usually cleared automatically after 30 minutes if spam traffic stops. Resending the message might also work right away if the message goes through a different server chosen randomly. However, it is recommended to wait for at least 30 minutes before attempting to send the message again

5.7.1 Message Rejected as spam by Content Filter

This error is not generated by the McAfee Email Protection service. This error is commonly enforced on the firewall or Microsoft Exchange server with specific Content Policies.

5.7.1 Recipient not authorized, your IP has been found on a block list

This is not an error generated by the McAfee Email Protection service. This error indicates that the receiving server has an IP level block list in place. This list may be found at the router, firewall or mail server level. If this error is being received, the receiving server must investigate possible block list entry at any one of the entry points to delivering the email message. Adding the sender/recipient to your McAfee Email Protection Allow List will not resolve this issue. 

5.7.1 SPF Not Authorized

This is not an error generated by the McAfee Email Protection service. This indicates that the receiving server is utilizing SPF validation to ensure mail senders match SPF records. If the server is an inbound server receiving filtered mail from McAfee, the SPF checking should be disabled on the server. If this is a message being sent outbound through the McAfee Email Protection service, then the SPF record for the client will need to be modified to include McAfee as an authorized sender.

5.7.1 Unable to Relay

This is not an error generated by the McAfee Email Protection service. This indicates that the receiving server is misconfigured to believe that email is trying to be sent through it instead of received by that server. It is necessary to contact the System Administrator for the receiving server to resolve this issue. 

530 Validating Sender

This error often occurs when the receiving mail server does not respond to the rcpt to: command when initiating an SMTP transaction. Verify that the receiving server is in a valid state (no error, no Back Pressure, mailbox exists). 

550 Backend Replied

This is the message provided when the McAfee Email Protection service receives a response from the receiving server during mail delivery. The message will be formatted often as 550 Backend Replied (message ID): (Message from server). With an error code of 550, this indicates that the receiving server has rejected the message due to some reason. Further information is available in the Non Delivery report. This is not an error often that McAfee can resolve.

551 Mailhost is on our global blacklist

This indicates that the sender's IP/Domain has been added to a temporary blacklist maintained by McAfee due to malicious traffic being seen from this IP/Domain.

551 Sender is on domain's blacklist

This indicates that the sender is on the policy Deny List for the domain they are attempting to send to. Only the Customer Administrator for the destination domain can correct this by removing the entry from the Deny List. 

553 Cannot find OUTBOUND MX Records for domain

As with the 451 No MX Records Available, this indicates that DNS did not return MX records for the domain.  The difference is with a 553 error, the domain most likely did not resolve. This could be due to failure at the Authoritative DNS for the domain or that the domain has expired.

553 Mailbox is restricted

This indicates that the receiving domain is utilizing Explicit User Creation and the addressed recipient is not located within the Users tab within the domain's Control Console. The Customer Administrator for the receiving domain will need to add the addressed user to the Control Console for mail to be received. Refer to the Account Administration Guide for more information on User Creation settings. 

552 MS-Office file containing VBA macros found inside of the email

This is not an error generated by McAfee's Email Protection policies. Users report this is due to filtering enabled on certain Sonicwall firewalls that inspect email as it is delivered. Users report the following conversation within the TechNet Social Community has been effective in resolving this issue: http://social.technet.microsoft.com/Forums/en-US/exchangesvrgeneral/thread/82d5697d-66c7-4064-8e09-93b22664f612